about:config > toolkit.legacyUserProfileCustomizations.stylesheets > true
Settings/Options > Advanced > General > Config Editor... toolkit.legacyUserProfileCustomizations.stylesheets > true
Based on this project by ardiman: https://github.com/ardiman/userChrome.js Additionally based on the modified files by Endor8: https://github.com/Endor8/userChrome.js/
Copy from this projects
\script_loader\profile\ folder userChrome folder and userChrome.js file to \ PROFILENAME \chrome\ folder.Copy from this projects
\script_loader\firefox\ folder defaults folder and config.js file into Firefox main directory (where the Firefox executable is; or on macOS, inside the main executable, at /Applications/Firefox.app/Contents/Resources/). Edit
userChrome.js file to add custom scripts!With Firefox 62 and Thunderbird 68 an additional preference
pref("general.config.sandbox_enabled", false); has to be set inside config-prefs.js file. This is considered less secure by Mozilla and is only a temporary workaround, but at the moment it is the only way to run custom scripts using "method 2".
Where to find Firefox
startupCache folder?about:profiles > Local Directory > Open Folder, close Firefox and delete all files in startupCache folder.This is not the same 'profile' folder custom scripts and styles are stored in!
Where to find Thunderbird
startupCache folder?Windows
C:\Users\ USERNAME \AppData\Local\Mozilla\Thunderbird\Profiles\ PROFILE FOLDER NAME \Linux/macOS
Search for
startupCache folder on your hard drive.More info about startup cache removal (in German): https://github.com/ardiman/userChrome.js/wiki/Skriptcache
about:support > Application Binary (Path on your system) about:profiles > Root Directory > Open Folder or about:support > Profile Folder > Open FolderWindows
C:\Users\ USERNAME \AppData\Roaming\Mozilla\Thunderbird\Profiles\ PROFILE FOLDER NAME \Hidden files must be visible to see
AppData folder. Alternatively open %APPDATA%\Mozilla\Firefox\Profiles\ from explorers location bar.Linux
/home/ username /.mozilla/thunderbird/ profile folder name /Hidden files must be visible to see
.mozilla folder.Mac OS X
~\Library\Mozilla\Thunderbird\Profiles\ PROFILE FOLDER NAME \ or~\Library\Application Support\Mozilla\Thunderbird\Profiles\ PROFILE FOLDER NAME \\Users\ USERNAME \Library\Application\Support\Thunderbird\Profiles\Script collection by ardiman: https://github.com/ardiman/userChrome.js
Script collection by Endor8: https://github.com/Endor8/userChrome.js
Script collection by xiaoxiaoflood: https://github.com/xiaoxiaoflood/firefox-scripts/tree/master/chrome