Performance on my Macbook Pro is horrible. It will often peg the cpu so badly that the laptop appears to be locked up. This is a known issue which Mozilla has chosen not to address and instead seems to hope the switch to webrender will fix. I say "seems to hope" because the bug for the issue doesn't give confidence that the full cause is truly understood and specify exactly how a switch to webrender will fix it. Maybe Mozilla knows and has done testing but it certainly isn't reflected in the bug report.
Firefox on Android is bloated, slow and is a terrible UX experience. Mozilla obviously recognizes this because they have already announced an effort to completely replace it. There are other Mozilla provided browsers for Android which do perform better but they have a limited feature set compared to Firefox and don't meet my needs.