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 stopped 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; 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".
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