4.2.12 (2026.3.17)
* Stabilize and optimize moving of multiple tabs with tree structure, especially across windows. (by tkng, thanks!)
* Add "Unload this Tree" and "Unload Descendants" context menu commands corresponding to the native "Unload Tab".
* Allow to create new native group by dropping tabs onto any areas of another tab simply, with pressing Shift key. (Without shift key, you need to drop tabs onto the head area of another tab to create new group.)
* Reconstruct option to set UI direction of the sidebar as Regular/Inverted instead of Left/Right. "Regular" always works similar to Firefox's native vertical tabs.
* Show confirmation dialog correctly for closing multiple tabs in a fullscreen browser window on macOS.
* Show tab previews in tab-hover tooltip again. (regression on 4.2.8)
* Fix misdetection of drop position of tabs after tabs are rearranged. (regression on 4.2.7)
* Duplicate partially dragged tree at the dropped place correctly.
* Fix mis-ordering of multiselected tabs moved by drag and drop.
* Fix mis-sizing of tab bar boxes after extra contents are inserted via API.
* Fix too narrow width of group labels in the Photon theme.
* Don't show nonsense "+0" label for collapsed tab groups with no other member.
* Suppress needless animation effects when items are scrolled into the view.
* Expand tab group automatically when a collapsed tree in the group is expanded. You can deactivate this new behavior with a new expert option under the "Tree Behavior" section.
* Don't mistreat dropped URL as a native tab drop.
* Hide UI elements internally used and should not be exposed to users, even if the background screen of the sidebar has transparent color.
* Detect "head" area of the drop target tab correctly on RLT environment, to create new group by drag and drop.
* Fix wrong alignment of tab group labels on inverted mode.
* Fix wrong text direction and alignment of tab labels with LTR title on RTL environment.
* Suppress uncaught errors caused by already closed tabs or windows, around mouse operations, successor tab operations and caching of tree information.
* Fix links to MDN documents from changelogs. (by theluckystrike, thanks!)
4.2.11 (2026.3.3)
* Custom tabs for grouping (ext+treestyletab:group) are available again on Firefox 150+ which never supports injecting of scripts to addon-hosted contents due to the bug 2011234. See #2356 in Sidebery for more details of affections of the bug.
* Many improvements around features, performance, stability and maintainability by tkng. Thanks a lot!

4.2.10 (2026.2.18)
* Show new tab action selectors on both side of the new tab button correctly, when both container selector and relation selector are active. (by bb010g, thanks!)
* Restore tree of tabs certainly on crash recovery and/or manual restoration of the previous session. (by tkng, thanks!)
* Fix handling of closed tree restoration: multiple tabs of a closed tree are now restored with single action correctly. (by tkng, thanks!)
* Many performance improvements with optimizations (#3831, #3836, #3837, #3838, #3839, #3843, #3847 and #3848 by tkng. Thanks!)
* Some performance improvements with optimizations around reduced reparsing of JSON strings while dragging and reduced reflowing.
* Apply and update auto-sticky state of tabs correctly, even if they are specified by other addons. (by tkng, thanks!)
* Update custom tooltip text more correctly. (by tkng, thanks!)
* Many cleanup of codes for future maintainability. (#3832, #3833, #3835, #3844, #3849, #3851 and #3852 by tkng. Thanks!)
* Suppress errors from handling of successor tabs when a tab is closed before the successor information is updated.

4.2.9 (2026.1.20)
* Fix some possible memory leaks around closed windows, tabs, and removed elements.

4.2.8 (2026.1.9)
* Show collapsed group member tabs with the in-content custom tooltip, like Firefox natively does.
* In the in-content custom tooltip for a hovered collapsed tree, show favicon and provide ability to switch to the tab corresponding to the clicked tree item.
* Activate the custom tooltip in the sidebar area by default, for collapsed trees and groups, if we cannot render the in-content custom tooltip in the active tab.
* Allow pinning a tab by dropping after the last pinned tab, and allow to unpinning a tab by dropping before the first unpinned tab. This simulates behaviors of Firefox's native tab bar more naturally.
* Update appearance of group items to match to the native one more.
* Show collapsed members counter after the active tab in a collapsed group, even if it is the last member.
* Move dragged group correctly when it is dropped before any existing group.
* Don't break tree structure of grouped tabs by drag and drop of child tabs.
* Never show the drop area to pin dragged items if a tab group is dragged.
* Don't show broken favicon in UI for invalid PNG provided as a data: URI.

4.2.7 (2025.10.21)
* Fix ability to drop items before the first tab when there is no pinned tab.
* Increase the default delay to show the drop area for tabs to be pinned (500ms to 740ms: you can configure it with a secret option pinInteractionCueDelayMS).
* Prevent grayed favicons of restored tabs in the first window restored from the previous session explicitly.
* Treat discarded tabs as pended correctly, even if restoration from cache is failed.
* Hide "unload tab" context menu command for already discarded tabs, like Firefox does.
* Reduce needless re-rendering of virtually scrolled tabs when pinned tabs are scrolled.
* Update en locale to fix a typo by purplnecropanda. Thanks!

4.2.6 (2025.9.22)

• Add ability to pin/unpin tabs by drag and drop. Now you can drop pinned tabs below/between unpinned tabs, and unpinned tabs above/between pinned tabs. This simulates behaviors of tab dragging on Firefox's vertical tabs.
• Disallow to set the height of the pinned tabs area smaller than the height of a pinned tab.
• Use label text for the "new tab" command in the context menu on tabs same to Firefox's native one, if possible.
• Show dropdown list in options with colors more easy-to-read, on the dark color scheme.
• Expose the expert option to control the position of the context menu popup for native tab groups.
• Update ja locale by tkng. Thanks!

4.2.5 (2025.7.11)

• Support ability to keep the active tab in a collapsed group visible on Firefox 142 and later.
• Prevent to show simulated tab preview panel on non-tab items.
• Prevent "shaking" of pinned tabs when the height of the pinned tabs area is narrower than a tab.
• Restore ability to drop dragged items to the blank area of the tab bar. (regression at 4.2.0)
• API: Fix container assignment for extra tab contents below tabs by emmanuel-ferdman. Thanks!
• Update uk locale by Taron-art. Thanks!

4.2.4 (2025.6.26)

• In-content panels (tab groups menu and tab previews) handle events correctly. (regression at 4.2.3)
• Never mix reactions for custom dialogs even if multiple dialogs are shown at a time.
• Update uk locale by Taron-art. Thanks!

4.2.3 (2025.6.23)

• Context menu commands now works even if it is opened on a blank space (by joanbm. Thanks!)
• Add an expert option to activate/deactivate native tab groups management UI (corresponding browser.tabs.groups.enabled of Firefox itself).
• Scroll pinned tabs container when an out-of-view pinned tab become active.
• Remove dragged tabs from their group when they are dropped before a group header explicitly.
• Don't create needless new group when a last member is dropped before the next another group but the tab is not moved actually.
• Disallow to resize pinned tabs area size larger than required.
• Unblock user operations correctly after drag-and-drop of tabs across windows. (regression at 4.2.0)
• Treat focused or active tab as the context tab if the context menu is opened via the keyboard (ex. Shift-F10 on Windows).
• Accept more cases of dropped native tabs.
• Delete obsolete option to deactivate using of tab multiselection API.

4.2.2 (2025.6.9)

• Pinned tabs are rendered with expected position after rearranging by drag-and-drop. (regression at 4.2.0)
• Apply designed colors always for the "Sidebar" skin, even if the "Dark" color scheme is active. (regression at 4.2.0)

4.2.1 (2025.6.7)

• Scroll to the active tab correctly with disabled animation mode. (regression at 4.2.0)
• Detect sidebar position automatically even if the window is in a screen placed leftside of the primary screen.
• Scroll to the new active tab and keep it in the viewport more correctly even if there are going-to-be-collapsed and/or sticky tabs.
• API: a scroll type message now accepts a new parameter group to scroll the tab bar to the specified tab group.

4.2.0 (2025.6.2)

• Drop support of Firefox older than 139.
• Add support of native tab groups feature of Firefox itself. TST will create a new tab group of Firefox itself instead of modifying tree, when you drag a tab to the head side edge of another tab.
• Show muted state indicator and sharing state indicator (for microphone, camera and screen) at the position same to the one on Firefox's native tab.
• API: Some notification type messages (ex. tab-mousedown) can contain Firefox's tab groups as a tab (tree item). They have properties similar to regular tabs but there is one difference: they have "group" as the value of their type property.

4.1.11 (2025.5.29)

• Keep the height of the pinned tabs area resizeable even if it was shrunken to zero.
• Don't shrink the height of the pinned tabs area to zero at the startup after it was manually resized.

4.1.10 (2025.5.27)

• Invoke commands in the fake context menu (shown by Multiple Tab Handler addon and so on) correctly. It was regressed for a long time.

4.1.9 (2025.5.25)

• The height of pinned tabs container is now resizable by dragging. Double-click on the resizer restores the auto calculated height.

4.1.8 (2025.5.24)

• Update localized labels of the context menu command "Unload Tab".
• Fix misfocusing after "Unload Tab" is invoked.
• Revert "show closebox in tabs only for active or hover" behavior for inverted appearance mode for non-default sidebar position, to reduce stressfull jumping of tab icons and labels.
• Add a new expert option to control fallback behavior of collapsed descendants tooltip. (You can enfoce to show collapsed descendants with in-sidebar tab preview panel.)
• Add expert option UIs for fadeOutPendingTabs and fadeOutDiscardedTabs previously implemented.

4.1.7 (2025.5.16)

• Show closebox in tabs only when it is active or hover, like Firefox's native vertical tabs.
• Suppress tab preview panels while dragging.
• Move dropped tab correctly when a tab is dropped after a collapsed tree at the end of the tab bar.
• Highlight active tab correctly after the active tab is moved across windows by Firefox's native tab bar.
• Add "Unload Tab" context menu command simulating the one on Firefox 140. Two secret options fadeOutPendingTabs (corresponding to browser.tabs.fadeOutUnloadedTabs) and fadeOutDiscardedTabs (corresponding to browser.tabs.fadeOutExplicitlyUnloadedTabs) are also introduced.

4.1.6 (2025.5.7)

• Apply animation effect to expanding tree correctly.
• Open dialogs correctly even if the <all_urls> permission is granted. (regression at 4.1.5)

4.1.5 (2025.5.2)

• Suppress Ctrl-Tab/Ctrl-Shift-Tab specific reactions (redirection of tab focus to skip collapsed tabs through tab switchings), when a collapsed tab get focused by something outside of TST except Ctrl-Tab/Ctrl-Shift-Tab e.g. clicking on a native tab.
• Cyclic focus of tabs with custom keyboard shortcuts for "focus to the next/previous sibling tab" commands.
• Simplify implementation of the tab preview panel embedded in the content area.
• API: Notify tabbar-mousedown|tabbar-mouseup|tabbar-clicked instead of tab-mousedown|tab-mouseup|tab-clicked to other extensions by clicking on the indent area of each tab.

4.1.4 (2025.3.13)

• Match styling of sound-playing/muted button to Firefox 136 and later.
• Add a new option to show tab preview panel only in the sidebar area.
• Fix mismatched checked state with special permission.
• Add a mechanism to help collecting performance profile while initialization process.

4.1.3 (2025.1.16)

• Show tab preview panel with visible background color on macOS.
• Size tab preview panel in the contents area correctly on macOS Retina display. (regression at 4.1.2)

4.1.2 (2025.1.14)

• Avoid unexpected white background in the content area, when the Dark theme of Firefox is chosen with activate tab preview panel.
• Apply uniform styling of the "sound playing" button on all themes including Photon.
• Size tab preview panel in the contents area correctly, even if privacy protection is enabled (ex. privacy.resistFingerprinting=true.)
• Add a new expert option to configure offset of the tab preview panel, for environments with enabled privacy protection.

4.1.1 (2025.1.10)

• Switch UI direction on RTL environments (using language with right-to-left direction, like Arabian.)

4.1.0 (2024.12.25)

• Reconstruct UI of the bookmarks creation dialog to simulate behaviors of the native one more.
• Add ability to simulate tab preview panel on vertical tabs (requires the permission to run arbitrary scripts on webpages, aka "Access yuor data for all websites.")
• Render descendants of a collapsed tree with better appearance based on HTML list, when tab preview panel simulation is available.
• Revoke needless optional permissions when all features requiring the permission are disabled.
• Add a new expert option to open dropped links in background tabs with discarded state.
• Accept dropping of tabs and links onto the new tab button, like Firefox does.
• Update styling of the sound playing state button in tabs to match to the native one on recent versions of Firefox.
• Show a badge on TST's toolbar button and open the initial startup page by clicking of it, when it is the first time of TST installation, as a failsafe of the suppressable notifications.

4.0.25 (2024.11.11)

• Fix disability of get-tree API for other addons and disability of tree view in group tabs. (regression at 4.0.24)

4.0.24 (2024.10.29)

• Never store raw URL of tabs to save user privacy. Tab URLs were stored just to associate effective favicon URLs with tabs (so they were not sent to anywhere), but today, favicon URLs are exposed to addons as data: URIs and on most cases there is no need to store effective favicon URLs. On required cases, only hashed strings are stored instead of raw URLs.
• Never cache tree of private windows, to save user privacy.

4.0.23 (2024.9.11)

• Remove dependencies to CSS2 system colors deprecated at letely versions of Firefox.
• Set text/plain drag data for shift-dragged tabs. Now you can drop tree items to any text input area.
• Update overflow state of labels for recycled tab elements more certainly.
• Reduce misdetection of tab closing/moving operations as internal operations.
• Open options page from group tabs, in a foreground tab with no error.
• Use text and bg colors of tabs same to Firefox's native tab bar on Windows 11. There is a difference v.s. the native tabs: colors of sidebar UI won't become pale in inactive windows.
• Improve integration for bookmarks creation from drag-and-dropped tabs: Save tree structure to bookmarks even if they are dragged from Friefox's native tabs, but don't create new folder if dragged with no tree structure (flat tabs) whether from native tab bar or TST's sidebar.
• Add ability to deactivate auto-grouping of bookmarks from dropped tabs with tree structure.
• API: Add new notification type try-scroll-to-activated-tab to block auto-scrolling to the activated tab.
• API: Expose a new tab state stuck as a part of tree item. It indicates that the tab is shown as stuck on an edge of the sidebar.
• API: Deactivate tab tooltip completely when a blank text is registered with high priority.
• Update nl locale by Vistaus. Thanks!

4.0.22 (2024.8.9)

• Fixup tree correctly after multiselected tabs are moved together by drag and drop on the horizontal tab bar or the Move Tab Hotkeys.
• Synchronize throbber animations after the sidebar is reopened.
• Keep highlighted appearance of multiselected tabs after the sidebar is reopened.
• Track and update overflow/underflow state correctly even if legacy overflow/underflow events are disabled completely.
• Restore "sticky" state of tabs correctly after tree restoration without cache.

4.0.21 (2024.8.4)

• Activate tree parent based on the user configuration more certainly if possible, when multiple tabs containing active are closed by one action.
• Allow to close a group tab opened to replace a closed parent, when it is closed repeatedly. This behavior can be deactivated and you can keep such tabs unclosable like as old versions, with setting a secret option closeParentBehavior_replaceWithGroup_thresholdToPrevent to -1.
• Reduce flashing of the vertical scroll bar on edge cases of overflowing.
• Don't place new child tabs opened from a pinned tab at odd location, even when there is any waiting-to-be-grouped tabs and the system is slow.
• Keep structure of grouped tabs as possible as we can, when partial tabs in existing trees are grouped via the group-tabs API.
• Suppress flashing of the scrollbar on an edge case with the Photon theme.
• Ignore mouse clicks only on animated closing tabs more certainly, to prevent detection of those clicks as ones on the blank area of the tab bar.
• Determine to apply multi-column layout (or don't) to the tree in a group tab more robustly, even if its appearance is modified by the user style sheet.
• Expose expert options temporarily when the options page is opened from internal links and the referred option is hidden as an expert option.
• Link to the suitable option to deactivate the behavior, from a group tab opened to group children of pinned tabs.
• Don't check the checkbox to control middle-click-paste on the new tab button, when the permission is granted but internal option is still deactivated.
• Suppress error from missing dataTransfer of drag-and-drop events.

4.0.20 (2024.6.28)

• Fix initialization failure from unhandled IndexedDB errors.

4.0.19 (2024.6.24)

• Defer scrolling to the successor active tab until the mouse pointer leaves from the sidebar area, if the successor is chosen by something feature like browser.tabs.selectOwnerOnClose out of the visible area. You can disable this behavior by setting deferScrollingToOutOfViewportSuccessor to false.
• Activate explicitly specified successor tab if possible, after multiple tabs are moved across windows by drag-and-drop.
• React to "Simulate Up/Down/Left/Right Key on Tree" keybaord shortcuts as tree available, even if the sidebar panel is opened in a separate window by Tree Style Tab in Separate Window or someone.
• Add ability to control temporary state of group tabs opened by API.
• Never insert extra contents to non-tab elements in non-target windows via API, if the target window is explicitly specified.

4.0.18 (2024.6.13)

• Add "Close Duplicated Tabs" context menu command to simulate the command of Firefox 127 and later.
• Change default shortcut to simulate arrow keys on tree for macOS: Alt-Shift-Uo/Down/Left/Right to MacCtrl-Shift-Uo/Down/Left/Right.
• Right/down arrow keys simulation now fallbacks to "focus to the next tab" correctly while the sidebar is closed.

4.0.17 (2024.6.10)

• Fix misindentation of tabs immediately moved after opened. (regression on 4.0.16)
• Fix misindentation of deeply nested tree on the startup. (regression on 4.0.16)

4.0.16 (2024.6.9)

• Add new keyboard shortcut slots "Simulate Up/Down/Left/Right Key on Tree" and assign default shortcuts Alt-Shift-Up/Down/Left/Right. They provide both spatial focus move on faviconized tabs and collapse/expand tree like arrow keys on tree items.
• Add new keyboard shortcut slots "Collapse Tree or Focus to Parent Tab" and "Expand Tree or Focus to First Child Tab" to simulate Left/Right Arrow keys on tree items.
• Wheel scrolling on pinned tabs and keyboard shortcuts to scroll the tab bar with focused pinned tab now scroll regular tabs if the container of pinned tabs is not scrollable.
• Optimize operations to track updated overflow/underflow state.
• Better drag and drop of tabs/trees across windows: the tree structure is kept better, temporary group tabs are kept, and moved tabs are kept discarded.
• Move focus to the parent tab as configured, when a last child tab is closed after it was reopened.
• Reduce needless animation effects unexpectedly re-applied to tabs rendered while virtual scrolling.
• Fix unexpected classes on tabs in the sidebar which are left by misordered operations.
• Fix unexpected infinit loop (caused increasing of CPU usage and blocking of GC) triggered by extra tab contents above/below individual tab.
• Update zh_CN locale by NightSharp. Thanks!
• Update ru, de and en locales by vadcx. Thanks!

4.0.15 (2024.5.21)

• Treat drag and drop of a parent tab to its descendant as a dragging of an individual tab and attach it to the drop position, even if the default action is configured to drag the whole tree. You can deactivate this behavior and prevent dropping of a parent tab to its descendant to turn the hidden option moveSoloTabOnDropParentToDescendant to false.
• Don't inherit container to an opened tab if it is opened by "Open in Container Tab" => "No Container" inin the native tab context menu.
• Never use overflow and underflow events to become compatible with Firefox 128 and later.
• Add new keyboard shortcut slots for "Toggle Tree Collapsed" and "Toggle Tree Collapsed Recursively" commands.
• Add a new option to show/hide TST's context menu commands on the native tab bar.
• Become more robust for cases that tabs are opened while the initialization process.
• Fix odd behavior after rendering error when the sidebar panel is shown with zero-width.
• Show container marker with thin width even if tabs are shown with expanded height.

4.0.14 (2024.4.17)

• Allow to detach tab from window even if the source window is maximized or fullscreen. (regression on 4.0.13)
• Prevent unexpected jumping of tabs on scrolling, when tab height is expanded by extra tab contents above/below tabs provided by helper addons.

4.0.13 (2024.4.10)

• Apply new-tab-command-tab behavior correctly. (regression on 4.0.12)
• Use GrayText instead of ButtonText as the tabs border color in the "High Contrast" theme, to reduce stresses from too high contrast.
• "Move Tab" => "Move to New Window" in the context menu on the sidebar now moves whole tree always.
• "Move Tab" => "Move to New Window" opens a new window shifted from the source window a little.
• Don't deactivate unrelated options even if <all_urls> permission is not granted.
• Fix unexpected reloading of the sidebar panel on tab attaching/detaching.
• Add a new secret option syncActiveStateToBundledTabs to suppress expanding of the tree and scrolling to it for group tabs bundled to a pinned tab, when the pinned tab become active.

4.0.12 (2024.4.5):

• Calculate tab dimensions more correctly. (regression on 4.0.11)
• Fix ability to override tab size with --tab-size.
• Use ButtonText instead of ButtonShadow as the tabs border color in the "High Contrast" theme, for better visibility.
• Don't apply new-tab-command-tab behavior for non-new-tab-command-tabs accidentally, e.g. tabs opened by other applications.

4.0.11 (2024.4.3):

• Optimize tab rendering more.
• Optimize updating of tab indentations on animation-disabled mode.
• Never show different "extra tab contents" in reused tab elements.
• Show favicon of a tab correctly when a favicon-less page is loaded.
• Apply the behavior option correctly to group tabs opened for tabs from bookmarks.
• Allow to set details options about tab rendering per each device.
• API: Cache tabs returned via API for better performance. It is disabled by default via an option cacheAPITreeItems.
• API: Show extra tab contents on the target pinned tab correctly.

4.0.10 (2024.3.21):

• Don't shift tree structure after a restart for a major update of Firefox (See also: how to restore correct tree from shifted tree)
• Show context menu items enabled by the option correctly.

4.0.9 (2024.3.20):

• Middle-click on the "New Tab" button opens a blank new tab if the clipboard is not accessible due to some reasons.
• Fix incompatibility with other addons closing initial tabs while TST is initializing (ex. Tab Session Manager and Firefox Multi-Account Containers).
• Apply user style sheets prior to built-in style rules correctly.
• Introduce new expert option to expose hidden tabs by other addons, and add expert options UI for the number of pre-rendered pages and visibility of hidden tabs.
• Suppress some non-critical errors while initializations.
• Update zh_CN locale by NightSharp. Thanks!

4.0.3 (2024.3.13):

• Fix miscalculation of drop position on tabs on the "Photon" theme.
• Expand height of the container of pinned tabs more correctly on edge cases.

4.0.2 (2024.3.13):

• Fix performance degression around detection of tab label overflow state.
• Fix needless blank space below last tab on the "Photon" theme.
• Fix blank dialogs when the "Access your data for all websites" permission is not granted.
• Hide unexpectedly shown menu items in the context menu.
• More respect labels of menu commands in the context menu on blank area of the tab bar.
• Update zh_CN locale by NightSharp. Thanks!

4.0.1 (2024.3.8):

• Tabs containing sticky tabs are kept expanded when another tree is expanded, even if those tabs are sticked via API.

4.0 (2024.3.7):

• Improved performance on cases with large number of tabs. Now tabs only in the viewport are rendered.
• Introduce new context menu commands and other triggers to stick arbitrary tabs to edges of the tab bar. It is similar to "Pin/Unpin Tab" but sticked tab keeps its tree.
• Indicate sharing state of tabs (camera, microphone and/or screen) with icons.
• Show dropshadow before normal tabs when the tab bar is scrolled.
• Show dropshadow after normal tabs when the tab bar is not fully scrolled.
• Use cached tree structure information more aggressively on Firefox startup, if the number of tabs, pinned status, and containers are matched.
• Add ability to control tabs opened from Firefox View.
• Suppress bookmarks folder auto creation for bookmarks from tabs, when multiple bookmarks are copied via the Library or something way.
• Move descendant tabs also correctlyfollowing to their parent, when a parent tab is moved to the top level via Firefox's horizontal tab bar.
• Apply the option to place opened tabs next to the last related child correctly, when multiple tabs are opened from a pinned tab.
• Avoid unexpected restoration of blank dialog windows by Ctrl-Shift-T on Firefox 116 and later.
• Restore tree structure more correctly for reopened tabs which were closed at a time.
• Lock scroll position temporary when a tree near the tab bar end is collapsed, just like as the case when tabs are closed.
• Open local files in tabs with blob: URL when they are dropped to the tab bar, instead of simply ignored.
• Never create needless multiple folders for bookmarks created from tabs tree.
• Most options are now treated as expert options and hidden by default.
• Many API improvements.
• Most of improvements at this version is sponsored by the Waterfox project / BrowserWorks Ltd. Many thanks to Alex Kontos! (Announcement blog entry at Waterfox project)
• See also histories section of the project page or the release page on GitHub to get full changelogs.

3.9.22 (2024.1.31):

• Fix failed initialization when an optional permission "Read and modify bookmarks" is not granted. (regression on 3.9.21)

3.9.21 (2024.1.26):

• Fix performance regression on 3.9.20 with on-memory cache.
• Prevent unexpected slicing of built-in icons in group tabs.

3.9.20 (2024.1.18):

• Drop support of Firefox older than 115.
• Restructure options about new tab position control, to reduce overlapped effects of multiple options. Now you can choose "open tab as a first/last child" for each option directly.
• Expose expert options to control behavior of new tabs opened from links and the "New Tab" command in the simulated tab context menu.
• Use on-memory storage for the cache of sidebar contents, to prevent bloating of Firefox's session file. This means that initialization on the browser startup takes more time, and you can take the old behavior back by a new advanced option.
• Guess tabs opened by the "New Tab" command more certainly.
• Suppress too much RAM usage problem with some themes with animations. (See also the bug 1875100.)
• Store device ID more safely for the simulated Sync feature.
• Update zh_CN locale by NightSharp. Thanks!

3.9.19 (2023.11.20):

• Don't reopen tabs with URL unopenable with addon's permission (local file, about: URL and so on) even for container inheritance.
• Deactivate "Open in New Container Tab" context menu command for tabs with unreopenable URL.
• Use icon color same to Firefox 120.

3.9.18 (2023.11.10):

• Add context menu commands and keyboard shortcut slots "Mute/Unmute this Tree" and "Mute/Unmute Descendants".
• Increase default interval of the heartbeat between sidebar pages and the background page from 1sec to 5sec for less CPU usage.
• Optimize performance of updating maximum tree level on situations with disabled animation.
• Determine color of SVG icons for the platform color mode (dark or bright), based on the CSS prefers-color-scheme feature.
• Update fr locale by cayenne17. Thanks!

3.9.17 (2023.9.8):

• Handle tabs internally moved by TST itself more correctly. Reduced wrong placements of tabs opened from a pinned parent on some situations.
• Optimize initialization process of the tab context menu on the sidebar page. Reduced delayed update of menu items after the menu appears on the screen.
• Reduced visual gap between the last tab and the new tab button in a scrollable tab bar with the Proton theme.
• Successfully detach a tab to a new window when a tab is dragged, moved to streight left or right and dropped at undroppable location, more certainly. The operation was unexpectedly blocked by a workaround for an old issue already fixed at Firefox 71.
• Treat dropped multiselected tabs from Firefox's native tab bar as dropped tree items.
• Update link to the list of known helper addons: now it is an wiki page.
• Introduce a workaround for a platform specific problem: unexpected reaction for drag events is triggered after a finished drag-and-drop actions.
• API: Add new notification type try-collapse-tree-from-collapse-command and try-collapse-tree-from-collapse-all-command to allow blocing of collaption of tree by commands.
• Updated style definition of tree twisties: now their positioning can be customized with margin and padding more easily.
• Uniform to label the feature to apply custom user style definitions as "User Style Sheet".
• Update ru locale by wvxwxvw. Thanks!

3.9.16 (2023.7.21)
* Reduce RAM usage around favicons.
* Right-click on the "new tab" button now opens containers selector like recent versions of Firefox.
* Expand ancestors tree while a tab is moved by Ctrl-PageUp/PageDown for better usability.
* Keep tabs scroll-locked even if the cursor is moved while the last tab is being removed.
* Keyboard shortcuts to move focus to next/previous sibling now cycles focus between sibling tabs.
* Add a new expert option to put tabs under a group tab always, even if they are opened from a bookmark folder and already organized as a tree. On such situations TST suppresses opening a group tab, because the group tab was initially introduced just to organize flat tabs opened from a bookmark folder as a tree.
* Attach child tab to the opener tab correctly even if the opener had no child and "when a tab is opened from existing tab, open it as: a child of the parent tab, next to the recently opened child" is chosen.
* Create bookmark item for the first group tab correctly, if there are multiple root level group tabs in the selection.
* Use bright border color for "drag and drop" options on the dark mode.
* Match styling of active and highlighted tabs on Proton theme, for Firefox 102 and later.
* Render box-shadow of the active tab on Proton theme more similar to Firefox's native tabs.
* Update de locale by juwbr. Thanks!
3.9.15 (2023.3.24)
* Never reload infinitely after tabs are detached from a regular window to a popup window (by Popup window or someone).
* New blank tabs reoepend with the container inherited from the active tab are activated correctly.
* Increase heartbeat interval automatically between sidebars and the controller, to prevent unexpected disconnection on cases where very large number of tabs. This introduces a side effect: the toolbar button and the keyboard shortcut to toggle the sidbar visibility may requrie more delay when there are large number of tabs.

3.9.14 (2023.3.13):

• Better simulation of browser.tabs.selectOwnerOnClose on slow environment.

3.9.13 (2023.3.12):

• Better handling of new blank tabs opened as a child of an active pinned tab, when child tabs from pinned parent are controlled.
• Better simulation of browser.tabs.selectOwnerOnClose for tabs opened by other applications.
• Add a new simulated option for Firefox's built-in "When you open a link, image or media in a new tab, switch to it immediately" about dropped links.
• On Windows 11 and other environments, shift sidebar contents without hovering by default to avoid covering scrollbar on tab UI.
• API: Add new notification types try-expand-tree-from-expand-command and try-expand-tree-from-expand-all-command to allow blocking of expansion of tree by context menu commands "Expand this Tree recursively" and "Expand All".
• Update ru locale by wvxwxvw. Thanks!

3.9.12 (2023.1.7):

• Allow to close tabs via group tab pages (middle-click or closeboxes.)
• Reduce flicker while updating tab list in group tab pages.
• Accept multiple URLs for new tabs (to support new tabs on both regular and private browsing windows.)
• Better synchronization of loading throbbers (by Lej77, thanks!)

3.9.11 (2022.12.6):

• Group tabs not from bookmarks with user's choice correctly. (regression on 3.9.8)
• Enlarge input fields for some options to input numbers.

3.8.26 (2022.7.15):

• Make some user styles written for old versions of TST effective. See the related issue also for more details.
• Prevent zoom-in/out by pinch-in/out on macOS.
• Add a secret option enableWorkaroundForBug1763420_reloadMaskImage for an ability to deactivate a workaround for the missing icons problem.
• Update ru locale by wvxwxvw. Thanks!