Probably silly, but I pretty much only use Chrome for the custom/compact title bar on Linux. On smaller screens it gives me more vertical on the content.
I've hidden window title bars for years, even on a full-size monitor; on a smaller screen it makes even better sense. Gives more vertical room for content in any application :-)
(Btw, with title bars hidden Firefox and Chrome actually have pixel-for-pixel same size nagivation elements, at least with Ubuntu's defaults – of course only when you toggle on system title bars in Chrome.)
It landed in Nightly as a WIP feature, but it's getting there: https://bugzilla.mozilla.org/show_bug.cgi?id=1283299