ゲームが重くなる問題はこの2つの設定をfalseにすると解決するが、
俺環ではどちらか1つだけfalseでも大丈夫なようだ
自己責任で

gfx.webrender.dcomp-texture-overlay-win
gfx.webrender.layer-compositor

After updating to 149, my browser games have started freezing during rendering. : r/firefox
https://www.reddit.com/r/firefox/comments/1s54bf9/after_updating_to_149_my_browser_games_have/

https://www.firefox.com/en-US/firefox/149.0beta/releasenotes/
> The WebRender layer compositor is now enabled on Windows,
> reducing power usage during full-screen video playback and improving WebGL/WebGPU performance.