It's probably well known at this point, but it doesn't hurt to spread the word further. Disabling accessibility services in Firefox (both on desktop and mobile, but specially on mobile) helps A LOT with performance and RAM usage.
Just set accessibility.force_disabled to 1 in about:config and enjoy the up to 20% less RAM usage and 5% less CPU usage (at least in my not so detailed testing on my laptop).
In my case my system went from 7.9GB to 5.2GB with the same tabs and windows open and from 25% to 20% CPU usage while having one of those tabs playing a livestream.
Quoting one of the comments in the Reddit thread I found this out to why this isn't disabled by default:
Accessibility does not start by default, but it starts lazily if another piece of software on your device starts requesting accessibility features from Firefox.
Unfortunately a lot of third-party software likes to do this even though they have nothing to do with assistive technologies.
You can also vote on this bug in Bugzilla to help it get solved faster.
I know. A wise decision imo.