You can forcefully disable hardware acceleration, that removes a few bits - though javascript can still guesstimate your CPU and memory.

For a more proper solution, you could try to convince Mozilla that granting every website uncapped multi-threading and direct GPU access is a bit much. If webgl/webgpu truly is a must, then maybe each website permission should start with a single-threaded software-renderer that behaves indistinguishable on all supported platforms. And only after granting the website that extra permissions let it determine that a more powerful GPU is available.