How to remove tab bar in Firefox

remove-tab-bar-firefox

# when you installed the Tree Style Tab in your Firefox Quantum or any newer, 
# you don't need the FX's Tab Bar anymore, therefore:

1. Click help -> Troubleshooting Information -> next to "Profile Directory " click "Open Directory".
  (if you can't see the menu, click the "wrench" icon on the right, then  Help and Troubleshooting Information )

2. Create (if not exists) a "chrome" directory

3. Create (if not exists) "userChrome.css" file and edit it

4. Put this line (if not exists)
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

5. Add this line below:
#tabbrowser-tabs { visibility: collapse !important; }

6. Restart Firefox

Hi Konrad
Thanks, but this doesn't work in MacOS, FF 57.0

@dvska, oh, sorry to hear that :( I thought it will work everywhere o.O