On Linux if you learn shortcuts for close/minimise/maximise as well, you can even remove window borders and title bars entirely. It's free screen real estate.
The gnome window title bars are obnoxiously thick and useless by default tho. I've found that Unity or even just Windows like styling in Gnome is a lot more respectful to your screen real estate.
I honestly don't know if there is a standardized way to pass the information or if it depends on the brand. I remember in the earlier version of gnome I had on my lenovo yoga the visual keyboard would popup on most text box but not on firefox which obliged me tolo use Gnome Web / epiphany when in tablet mode but they sorted it out later. I think there wasn't a tablet mode per se but I had used gnome tweak or an extension to have the accesibility options easy to access and enable the visual keyboard but it may have been mpre automatic later. I am saying all this out of memory because that computer died 2 years ago and I didn't use the tablet mode enough to replace it with similar one.
Is firefox actually fully integrated with gnome/gtk, or does it rely on some form of adaptor?
I've recently installed kde on one of my laptops (I usually use i3) and firefox is pretty wonky there. For example, with the OOB configuration, if I double click the top border of a window, it will maximize vertically. Firefox seems to ignore that. It does fully maximize if I double click the title bar, though.
Right and middle clicking the maximize button maximize horizontally and vertically with KWin and that does work with Firefox. Hard to say which part is to blame with i3 + Firefox. But it's not that Firefix needs Gnome.
I used to use "GTK Title Bar" gnome extension which was abandoned a few versions ago so had to write my own and it's X11 specific. The one drawback is that when windows are reopened, they are offset by the title bar height i.e. it messes up whatever is tracking the size/offset/location.
Anyone have other ways to do this in gnome and do they work on wayland too?
I'm on Fedora KDE so won't be much help to you, but there is a "Windows Rules" section in the system settings where I've added a rule that applies to all windows with the property "No titlebar and frame". Actually I'd quite like frame just with no titlebar, but that's not an option.