Simple Tab Groups works across browser instances/windows too. If you select a group in another window, the selected window will jump to the foreground with the chosen group selected. You can even select the specific tab within that group in background browser windows. GIF example Functionality / development notes:

New design implementation
Dark theme added
Added colored group icon
Added the ability to import the backup groups of the old extension Tab Groups
Added support of the Mozilla extension Firefox Multi-Account Containers
Now fully supports multiple windows
Saves last active tab after change group
Show currently used group in icon (see screenshot)
NOT supported: Private (Incognito) Mode
Added ‘close tab’ by middle-mouse click
Added simple switching between groups and tabs in search mode using the up, down, right, and left keys
"Manage groups" functionality
Added Drag&Drop support for tabs and groups in popup window
Added support sorting groups (context menu in popup window)
Added field for search/filter tabs in "Manage Groups"
Added support to Backup/Restore tabs, groups and settings to/from json file
Custom group icons, set group icon from tab icon (by context menu)
Added Undo Remove group by context menu browser button (see screenshot)
Added support for catch tabs by containers (#76)
Added dark theme
Added support SideBar

REQUIRED for dark theme: Set svg.context-properties.content.enabled to true in about:config page. How to do this. Permissions used:

tabs: for tab management
tabHide: for hide tabs
contextualIdentities & cookies: to integrate with Firefox Multi-Account Containers
notifications: for notification on move tab to group etc.
menus: for creating tabs context menus
sessions: for save session data (last used group, etc.)
downloads: for creating auto backups
management: for automatically detect the required addons
storage: for saving groups locally
unlimitedStorage: restore tabs after close window, there can be a lot of tabs
<all_urls>(Access your data for all websites): for tab thumbnails and catch/move/reopen tabs in needed containers/groups
webRequest & webRequestBlocking: for catch/move/reopen tabs in needed containers/groups
(optional) bookmarks: access for create bookmarks

How to integrate with the Gesturefy extension You have to input the following into Gesturefy: Add-on ID: simple-tab-groups@drive4ik Parse message: On Supported actions:

{"action": "add-new-group"}
{"action": "rename-group"}
{"action": "load-next-group"}
{"action": "load-prev-group"}
{"action": "load-next-unloaded-group"}
{"action": "load-prev-unloaded-group"}
{"action": "load-history-next-group"}
{"action": "load-history-prev-group"}
{"action": "load-first-group"}
{"action": "load-last-group"}
{"action": "load-custom-group"}
{"action": "delete-current-group"}
{"action": "open-manage-groups"}
{"action": "move-selected-tabs-to-custom-group"}
{"action": "discard-group"}
{"action": "discard-other-groups"}
{"action": "reload-all-tabs-in-current-group"}
{"action": "create-temp-tab"}
{"action": "create-backup"}

This extension may conflict with other programs similar in functionality. Conflicted extensions include, but may not be limited to:

Tab Open/Close Control
OneTab
Tiled Tab Groups
Totally not Panorama (Tab Groups with tab hiding)
Panorama Tab Groups
Panorama View
etc.

Please — help me translate this extension into your language! This extension also has these plugins: