Interesting - I have no experience with this, but Firefox does have an
option to disable the default hardware acceleration, and some sites
recommend this to solve performance problems:
https://lifehacker.com/disable-firefoxs-hardware-acceleration-to-fix-slowness-749344037
https://support.mozilla.org/en-US/questions/1050822
In my Firefox, the setting is under Preferences, section Performance,
uncheck "Use recommended performance settings", and then you'll find a
(checked by default) checkbox labeled "Use hardware acceleration when
available". You can try unchecking it and see what happens.
Celejar