I've tried several forks of mobile Firefox over the months and they all (Mull, Fennec, Iceraven) suffered from the same issue of running at 60 Hz while the regular app runs at the native 120. This makes it feel very sluggish especially in comparison to every other app and has kept me on the official app.
I've wondered if other people had the same issue or if it's related to my phone (Nothing Phone 1), and if there's a potential fix.
I don't have the same issue. Fennec from F-Droid runs at 120Hz even with tabs open
The indicator does flicker between 60 and 120 while the page is loading, but it's not perceptible. However, if what I'm seeing means the FPS goes down to 60 while the app is busy, this may be some kind of performance throttling done to keep resource usage low. If you have lower end specs, this may be the explanation. I'm on a Pixel 6 Pro.
Performance is a good lead since it feels lower than 60fps and my panel can only switch between 60/120 Hz. I wonder what could cause that to happen only on the forks since the regular Firefox is buttery smooth even on complex sites.