i did a comparison test between i.e., firefox and opera a couple years ago. i installed a fresh operating system each time and used each one exclusively for 3 months. they all ended up performing the same. each had a couple minor good points that the others didn't have, firefox worked better with linux apps and i.e. worked better with windows than firefox did. right now, allot of sites are optomized for i.e. because it's the most widely used, which makes them a little less efficient with firefox, which mozilla makes up for by not having so much overhead, but it's not as seamless with windows os as i.e., and some sites won't work with firefox at all, so the browsers all end up being pretty equil.
most of the people i know have trouble with fb from time to time, sometimes they can't get into their games for a day, sometimes the chat doesn't work, it's different problems. it's because fb is constantly updating the code, like last week when fb instituted the live feed and news feed views. that's a major change to the core of the fb system, so bugs had to be worked out for awhile. same with the games, they put in major core upgrades and then it takes awhile before the game is stable again.
it's not just you twirley :-)