I'm not experiencing the same issues in firefox as you are then. I loaded it up last night and everything seems to be running fine, and my firefox isn't even updated to the latest version I don't think, as it kept suggesting that I refresh it as it's been so long since I'd opened it - at least a year or so. 

I'll be sure to look for this slow down you all are talking about between 3 and 5 today. Is that eastern time? I'm on here every day and have not noticed a slow down, but I can't say I'm always specifically on at that time. Yesterday I was in town around that time.