Firefox 96.0 CPU usage

Latest updates (using 20.04) installed firefox 96.0 which, compared to 95.0.1, absolutely drains my CPU/battery on my laptop, particularly if decoding video. Is there some way to revert to the previous version - has anyone else had this issue?

I've noticed that webrender is not functional but I have no way of knowing if it was working previously.

This might have been caused by the nvidia DKMS not being loaded correctly after I reverted to 5.11.0-46 kernel when the update to 5.13.0-27 effectively disabled my laptop screen.

Turns out its something related to (or is) this: 1739259 - Snap, X11/dual GPU NV+Intel: Intel-only=ok (EGL as expected). NV on-demand + NV-only = "X11_EGL: broken by runtime: glxtest could not use EGL" + "glxtest: libEGL missing" (GLX as expected, but libEGL should not be missing)

Firefox doesn't recognise or use the GPU for WebRender when the nVidia "On Demand" setting is used within nVidia PRIMe; instead Firefox uses the AMD Renoir on my system which saps a lot more CPU. If I set nVidia PRIME to "Performance", then Firefox detects the GPU and CPU usage drops (also appears to overall improve heat when running Firefox).

Still investigating a workaround.