I wouldn't advise it in all honesty, I'm not sure how to bring them back (lol)
But I used this:
Hevilmystic
said
:
https://addons.mozilla.org/en-gb/firefox/addon/classicthemerestorer/
I believe I went into the options and ticked the one that said something about hiding tabs, and then I removed the address bar and it glitched and removed the whole top bar