OK, tried to use a couple. Some do come up with "not available for your platform" and the couple I tried to download timed out or gave a message about not being able to download at this time, try later. This is with SeaMonkey.
We're missing a lot more then just OpenGL. There's the web fonts that we all wish we had as well as H264+AAC. Then looking quickly at the source, I see, alarm, battery, bluetooth, camera, cell broardcast, datastore and devicestorage which we partially support, fmradio, gamepad, mobilemessage, power ,sms, telephony, time, voicemail, wifi. There's also accessing the accelerator, lock and screensaver support and I'm sure more. We also lost the shell functions (setting background, setting default browser) at one point.
Some of these don't make sense on the desktop, others I remember having to disable back in the 10esr era. Now looking at the obj-dir, most did compile but like camera, are missing an interface.