source: https://www.pcworld.com/article/823939/vertical-tabs-in-firefox-yes-its-really-possible.html
- open
about:config
in Firefox tab - in the search find
toolkit.legacyUserProfileCustomizations.stylesheets
and toggle value totrue
- open
about:support
- scroll down to the section that says “Profile Folder,” and click the “Open Folder” button
- Create a new subfolder called
chrome
within the folder you just opened - in the new
chrome
folder, create a new text fileuserChrome.css
- paste inside css file content from below, save and restart Firefox. Voila! It should work.
userChrome.css
, source: https://raw.githubusercontent.com/OneJaredNewman/firefoxcss/main/userChrome.css