Firefox tabs in multiple rows

  1. Go to about:config, enable config toolkit.legacyUserProfileCustomizations.stylesheets.
  2. Go to about:support > Profile Directory > Open Directory. Firefox profile directory will be openned in new window.
  3. In your profile directory, create folder chrome if not exist.
  4. Go to folder chrome, create file userChrome.css.
  5. Copy content from multi-row_tabs.css into userChrome.css.
  6. Restart Firefox.
firefox  css