Strangely, none of my coworkers seem to have problems. But every release seems to get worse; first it was terrible performance, then fonts in pages and the UI became blurry. This happens even on newly-installed MBPs, so it’s doesn’t seem like it could be related to anything I’ve done. And yet… coworkers don’t have problems.

A profile refresh is useless in this case.

Try a profile refresh

Tried. No success. I've also fully-uninstalled it with CleanMyMac, also to no success.

Why do you think a piece of software running on your laptop would behave differently from millions running on the same hardware. Profile, addon, custom install location, weird env variables

have you changed the resolution of your display to be "scaled" in system preferences? does setting it to "default for display" make FF usable again?

I keep it at scaled to max resolution, but I reverted to default and it made no difference.

If it affected everyone all of the time, it would have been fixed.

sierra (not high sierra) and latest 15/4c MBP.

Has been working just fine here for 7-9mo since I got it (not on the latest latest, but this sounds like an ongoing issue)

Agree it's weird.

I’m on a 5k iMac with zero problems on latest OS X.