just two cents here, as far as I know, all browsers need GPU acceleration.
you can try to turn it off see how fast you can browse.
so without OS, how can browser drive GPU?
Video acceleration and rendering acceleration are both mainstream.
On Chrome, open chrome://gpu which will tell you various things about its use of your GPU.
I'm not aware of an equivalent page for Firefox but opening about:support should somewhere inform you of the compositor, which when it says "WebRender" also makes use of your GPU.
Based on my previous knowledge, text, UI controls, video frames all have to go through the render pipeline. Should be no exception.
This is community talk, just fyi.