Running Firefox under Qubes has become increasingly frustrating, as tabs crash whenever (apparently?) they try to use WebGL, or anything that depends on access to a GPU. More and more, Firefox seems to depend on GPU access (or something?) and fails hard when it's not there.
To be fair, that sounds like a bug in the graphics driver or OpenGL ICD/libraries. GPUs are a bit special in that they have the power to hose your entire running OS (force a reboot due to a hard hang) no matter what OS you're running. It's just the nature of GPUs and how their drivers work... With direct access to memory and allowing user space applications access to their hardware features. In other words: Probably…
If I understand it correctly, that's one of the perks of WebRender: by using the GPU more like a game engine would, we're relying on code paths that tend to be better tested / more reliable.