Google Maps, I can confirm. It works, but it's noticably slow on Firefox. Tiles appear a tab bit slower, and street view navigation takes a fraction of a second to respond. It didn't stop me from using Firefox, but I can absolutely understand if someone finds it as a deal breaker if they use Google maps often.
Well I can't say I have ever experienced performance quite that bad myself. On my i7-2700K desktop I'm only seeing about 6s-7s each. Kind of hard to tell when maps is really finished loading though.
I share the experience with Maps, though I never see it these days as the G gets its own ungoogled-chromium sandbox and don't get to play with other domains here anyway.