Makes your firefox tabs and url bar smaller

Also allows to press tab close button when there are multiple opened tabs (on hover)

Without: With:

Set toolkit.legacyUserProfileCustomizations.stylesheets in about:config and move userChrome.css to YOUR_PROFILE/chrome/

On Linux ~/.mozilla/firefox/YOUR_PROFILE/chrome/

On Windows %APPDATA%/Mozilla/Firefox/YOUR_PROFILE/chrome/