I have a netbook that Firefox won't even try to launch WebGL on. Chrome seems to run WebGL just fine, though shaders with more than about twelve instructions fall off a performance cliff.
(Add one multiplication operation over the limit, and performance decreases twentyfold. Keep the new line, but delete any other single line of code in the shader, and performance goes back to normal.)
Poking around the Firefox wiki, it looks like it uses it's own native backends on basically every platform except Windows.
I have no idea whether any of this is relevant to the original Firefox support issue.
I don't have the machine in front of me, but it's an eee PC with I believe an Intel n550 CPU and an Intel GMA 3150 graphics chipset. I saw this behavior under a recent version of Ubuntu, probably 19.10.
(The "fast" framerate was something like one frame very 1-2 seconds, which was acceptable for running an image filter. The slow framerate was one frame every 30-40 seconds, during which Chrome locked up completely.)