Tree Style Tab

It always takes me two seconds to piece together the setup steps. Now it’ll only take me one.

Install Tree Style Tab.

Put this into ${YOUR_PROFILE_ROOT_DIRECTORY}/chrome/userChrome.css (that chrome directory will probably need to be created):

#TabsToolbar {
  visibility: collapse;
}

#titlebar {
  display: none;
}

Open about:config and set toolkit.legacyUserProfileCustomizations.stylesheets to true.