In Thunderbird (abbr as TB) 60, there are generally two ways to customize the UI:

Use CustomizeMyBird addon. Write code in chrome/userChrome.css under profile directory.

The first way is essentially the second way, only easier to use, and has live preview which means you don’t need to restart TB again and again to view what’s changed.

Since TB 68 was released recently, many people who upgraded to that version have found CustomizeMyBird stoped working due to incompatibility. Here I will introduce the migration steps to take for some typical scenarios you may encounter.

You placed all your customization code in userChrome.css

Congrats, your TB should look just as expected. If not, you only need to set the option toolkit.legacyUserProfileCustomizations.stylesheets as true in ConfigEditor, which can be opened from Preferences → Advanced → General → ConfigEditor .

You used CustomizeMyBird and tweaked without code

Currently CustomizeMyBird does not support TB 68+, and the author has no plan to do that. Fortunately the author created another repo called CustomCSSForTb, it’s a bunch of css files rather than a plugin, but most of CustomizeMyBird’s functionality should be involved. Check the project to see how to get it work.

You placed your customization code in CustomizedMyBird

The solution is simple: get the code and put them into chrome/userChrome.css . What may bother is how to get the code in the disabled CustomizeMyBird.

First you need to open the profile directory: click the three-line menu and follow Help → Troubleshooting Information , on the new page, click Show in Finder button besides “Profile Folder” line.

Then open prefs.js file and search for extensions.customizemybirdextension.customcsstb , you should find something like below:

user_pref("extensions.customizemybirdextension.customcsstb", "#threadTree treechildren {

font-size: 13px !important;

font-family: \"Helvetica Neue\";

}

#threadTree treechildren::-moz-tree-row {

height: 32px !important;

}

#threadTree treechildren::-moz-tree-cell-text(unread) {

color: #222 !important;

}



#folderTree treechildren {

font-size: 13px !important;

}



#folderTree treechildren::-moz-tree-row {

height: 25px !important;

}

");

Copy the second parameter of user_pref , print it in a console like Python or Node:

Python 3.7.1 (default, Aug 31 2019, 17:32:38)

[Clang 10.0.1 (clang-1001.0.46.4)] on darwin

Type "help", "copyright", "credits" or "license" for more information.

>>> print("#threadTree treechildren {

font-size: 13px !important;

font-family: \"Helvetica Neue\";

}

#threadTree treechildren::-moz-tree-row {

height: 32px !important;

}

#threadTree treechildren::-moz-tree-cell-text(unread) {

color: #222 !important;

}



#folderTree treechildren {

font-size: 13px !important;

}



#folderTree treechildren::-moz-tree-row {

height: 25px !important;

}

")

#threadTree treechildren {

font-size: 13px !important;

font-family: "Helvetica Neue";

}

#threadTree treechildren::-moz-tree-row {

height: 32px !important;

}

#threadTree treechildren::-moz-tree-cell-text(unread) {

color: #222 !important;

} #folderTree treechildren {

font-size: 13px !important;

} #folderTree treechildren::-moz-tree-row {

height: 25px !important;

}