about:config > toolkit.legacyUserProfileCustomizations.stylesheets > true
Settings/Options > Advanced > General > Config Editor... toolkit.legacyUserProfileCustomizations.stylesheets > true
M1 is based on this project by nuchi: https://github.com/nuchi/firefox-quantum-userchromejs M1 stoped working in Firefox 72! XBL support got dropped.
From this projects
\method 1\ folder copy userChrome folder and userChrome.css file to \ PROFILENAME \chrome\ or add code from userChrome.css file to an existing userChrome.css file.Edit
userChrome\userChrome.xml file to add custom scripts.
M2 is based on this project by ardiman: https://github.com/ardiman/userChrome.js
M2 is also based on the modified files by Endor8: https://github.com/Endor8/userChrome.js/
From this projects
\method 2\profile\ folder copy userChrome folder and userChrome.js file to \ PROFILENAME \chrome\ folder.From this projects
\method 2\firefox\ folder copy defaults folder and config.js file to Firefox main directory (where the Firefox executable is). 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".
M3 is based on this project by xiaoxiaoflood: https://github.com/xiaoxiaoflood/firefox-scripts
From this projects
\method 3\profile\ folder copy utils folder and userChrome.uc.js file to \ PROFILENAME \chrome\ folder.From this projects
\method 3\firefox\ folder copy defaults folder and config.js file to Firefox/Thunderbird main directory (where the Firefox/Thunderbird executable is). Edit
userChrome.uc.js file to add custom scripts or delete userChrome.uc.js file and add scripts directly into /chrome/ folder.
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
More info about startup cache removal (in English [Google translation]): https://translate.googleusercontent.com/translate_c?act=url&depth=1&ie=UTF8&prev=_t&rurl=translate.google.com&sl=auto&sp=nmt4&tl=en&u=https://github.com/ardiman/userChrome.js/wiki/Skriptcache
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
Script collection by Patchonn: https://github.com/Patchonn/firefox-theme/tree/master/userChrome