Hmm...that is super strange then. Intel has definitely been the most solid for me when it comes to GPU stability, including in Firefox. I primarily use a workstation with an AMD GPU, but have a secondary laptop with Intel and had no issues with Firefox there whatsoever. I am also on Arch. The only time I ever experienced frequent crashes was when I was testing the Wayland build early on, (they still happen sometimes on Wayland, which is still experimental in Firefox, but on X things have been solid for me).

I am honestly perplexed what the issue could be then, I was sure you were using an NVidia with the proprietary drivers or something like that, as such setups have caused me trouble in the past.

The only thing is I wouldn't recommend turning on WebRender for everything yet, but it's not on by default so I doubt you had it on.