> I'm looking for a way to have the tab bar hidden

1. Go to `about:config` and set toolkit.legacyUserProfileCustomizations.stylesheets true

2. Go to `about:support` and find your profile folder

3. Create subfolder `chrome` there

4. Create file `userChrome.css` in `chrome` folder

5. Put this text in it:

  #main-window #TabsToolbar {
    visibility: collapse !important;
  }