Unread Tabs Restorer Some Firefox users prefer to apply different styles to tabs depending on their status for clarity: unloaded, unread,... In the past there were extensions like Tab Mix Plus that do this but support for legacy XUL extensions was removed with the release of Firefox 57 in November 2017. Many legacy extensions, including Tab Mix Plus, were never upgraded to WebExtensions due to limitations of the new API. Nevertheless, it was still possible to style tabs depending on their status through userChrome.css:

    .tabbrowser-tab[pending] { /* Set styles for unloaded tab */ }
    .tabbrowser-tab[busy] { /* Set styles for loading tab */ }
    .tabbrowser-tab[unread] { /* Set styles for unread tab */ }

With the release of Firefox 61 in June 2018 support was removed for detecting unread tabs in userChrome.css [Bug 1453957]. At this moment the only way to restore this functionality is by injecting JavaScript in each tab page to change the tab title after loading the page. That is exactly what this extension does. The tab title change can be detected in userChrome.css with titlechanged. After installing this extension .tabbrowser-tab[unread] must be changed to .tabbrowser-tab[titlechanged] in userChrome.css:

    .tabbrowser-tab[pending] { /* Set styles for unloaded tab */ }
    .tabbrowser-tab[busy] { /* Set styles for loading tab */ }
    .tabbrowser-tab[titlechanged] { /* Set styles for unread tab */ }

Permissions Unread Tabs Restorer requires following permissions:

Access your data for all web sites
Access browser tabs

Why does this extension require access your data for all web sites? The unread functionality can only be restored by injecting JavaScript in all tabs. If you think this is unacceptable, please do not install this extension. If you want to know what exactly the extension does, download the extension xpi file, unpack it and inspect the content. Principle of operation The extension is less than 40 lines of code spread over 3 files:

background.js
tab_loaded.js
tab_activated.js

Script background.js executes tab_loaded.js when a tab is loaded in the background and tab_activated.js when a tab is selected. Script tab_loaded.js appends a hidden character to the tab title to trigger titlechanged that can be used in userChrome.css. Script tab_activated.js removes the hidden character again. Usage To use custom tab styles and Unread Tabs Restorer you must enable the loading of userChrome.css. This is disabled by default in newer Firefox versions:

Launch Firefox
Navigate to about:config
Search for toolkit.legacyUserProfileCustomizations.stylesheets and set it to true
Navigate to about:profiles
Locate the Root Directory of the profile in use and click the Open Folder button
Create a new folder named chrome
Create a new text file named userChrome.css in the chrome folder
Open userChrome.css in a plain text editor and paste following CSS styles:

    .tabbrowser-tab[pending] { color: red !important; }
    .tabbrowser-tab[busy] { color: dimgray !important; }
    .tabbrowser-tab[titlechanged] { color: blue !important; }

This will make the text of unloaded tabs red, loading tabs grey and unread tabs blue. Feel free to customize the styles to your liking. Finally restart Firefox to enjoy the new tab styles. Future There are no plans to add additional features to Unread Tabs Restorer. The extension was developed only to restore the lost functionality of unread tabs. The extension will become obsolete when Mozilla reimplements the unread tabs functionality or removes support for userChrome.css completely. Credits Unread Tabs Restorer is based on the Tab Flag extension by EffPeh. License Unread Tabs Restorer is published under the Mozilla Public License Version 2.0.