I had the same issue recently (since I actually have a working premium account again -- yay :dance: ) I thought it was related to my earlier problems and maybe it was. While logged in, I could see no chat at all, and in 2 or 3 minutes the memory and CPU would spike and crash the browser. The issue was Flash and it happened to any browser I tried. I uninstalled and reinstalled everything, cleared the cache, cookies, user data, everything. I had resorted to disabling flash in the browser I logged in with, and using another browser not logged in with Flash enabled for video. (if not logged in, the chat showed up normally -- but then no PM)
Lo and behold, MFC support actually answered an email of mine. They said -- you need Flash enabled, clear the cache and cookies and try again. So I did that and of course it has been fine since. I had done the same thing countless times before and the problem persisted. I doubt that MFC changed a setting on their end, but I am not sure how what I did that time was any different than what I had tried earlier. All I know is that the chat and everything else seems to be working normally again.