Got tabs working on the bottom of the page.
https://github.com/Okamoi/UserChrome...r-Windows7.css (works on Windows 10 too)
Create file called 'userChrome.css' and paste the above code linked in the above github site.
Create a new folder called 'chrome' in your FF profile folder (find it here:
https://www.reddit.com/r/firefox/wiki/userchrome).
Restart FF and tabs should should now be at the bottom of the page *where they belong*.