Proton is bad - Include Lepton

Nobody likes the new UI, it is generally hated and just bad, i won't bother listing all the one hundred reasons why it sucks, they already did that just fine: https://www.reddit.com/r/firefox/comments/nsjdb9/firefox_89_proton_feedback_megathread/

Please consider not doing that ugly bubble tab thingy. Here is Lepton: https://github.com/black7375/Firefox-UI-Fix and i think this should be included per default.