In the Firefox Release channel, WebRender is currently only enabled on Windows 10. Windows 7/8 support should be coming soon in Firefox 83 (2020-11-17) and macOS and Linux after that. As you say, GPU drivers are the biggest problem.
I have an Intel video card (UHD 630), and Webrender (which I had to forcibly enable) is working very well. Video acceleration, too. Even with a 4K screen.
See https://wiki.mozilla.org/Platform/GFX/WebRender_Where
To check if you're using webrender, check about:support. Check the graphics>compositing section.
(Edited to correct first paragraph.)