Just as Mozilla did in Firefox 59 (you can check it out in Firefox Nightly atm), and someone was doing for the Mac version in #12377, it would be really good to have an option to integrate the title bar in the same row where the tabs reside, in order to save some vertical space (which is even more important if like me you usually work on a non-FHD laptop such as an old Thinkpad or a Dell Latitude).

I said in Gnome cause it's what I use, but maybe it could be made into a more portable solution that has options for all DEs with top bars (be it Mac, Gnome, Xfce...). Like Mozilla did, it could even start to roll out when just some DEs are supported, with the warning that it may not work on all systems.