[Matterrr]

One extension I don't find a replacement for is Hide caption titlebar plus. It makes it so there's a permanent title bar even when Firefox is maximized. I had to change an xfce setting to hide the title bar when a window is maximized, meaning I lose the title bar for every application... Not ideal. Does anyone know if there is an argument to launch firefox without a title bar? Or set it in xfce for only one application?

[bkor]

Apparently client side decorations might appear in Firefox 59 at the earliest. For me having that negates the need to hide the title bar while maximized.

Under X11 there are various tools to hide the titlebar (entire chrome basically), see devilspie.

[chippy]

This is my favourite extension also. When using a laptop or other small screen, being able to remove the title bar is essential. I'm not upgrading to 57 until I can find a good workaround.

Apparently, one used to be able to manually modify Firefox's userchrome.css to do something similar, but I've yet to find descriptions on what to do with this new version of Firefox.

A different broken family of extensions that is impacted is mouse gestures, even for things like moving along tabs when hovering over them using the mouse wheel (default Chrome experience). I don't think this behaviour is possible with the new version of FF, sadly.

[r3bl]

userChrome.css is still present on Quantum. I haven't played around with it a lot, but if you feel like getting your hands dirty, this should be a relevant resource to you: https://github.com/Aris-t2/CustomCSSforFx/issues/1

[boriselec]

Sadly, GUI tweaks is very limited on new extensions api