I just got an Update from Mozilla for Firefox to Version 61.0 and since then WebGL needs crazy a lot of CPU-Ressources.
We testet all our demos, any your chair configurator on last firefx 61.0 and all works smoothly. Can you share all other harsware specs and OS? Have you tried to open demos on different PC in 61 firefox? Have you get the same result?
Co-founder and lead graphics specialist at Soft8Soft.
In my Case the Problem was this: Firefox was not able to get the performance from the graphic card, so the performance was adressed to the CPU. Which is a bad deal, even for 2 Xeons. If this is the Problem, it’s easy to find out: Just open the taskmanager and see how the high the GPU and CPU performance is. If the CPU is working really hard while using webgl in firefox, then maybe the graphic card-driver is not uptodate.