I'm there with ya. I take a medicine we call the "barbie drug" and sometimes we have to alter the dosage. We call it the "barbie drug" because it makes most people who take it not hungry and really forgetful. The only thing Barbie and I have in common is the hair - I'm all of 5 feet tall.... but I do have waist length blond-ish hair... and when we change my medicine - look out!!! Dumb isn't even the beginning of it. At first my boss thought it was a joke, but now she realizes how serious it can be. When we find accounting mistakes I make (I work in the accounts payable department - oops) sometimes they are minor - and sometimes not.... We just have to laugh - because there isn't much else we can do!! When we find a mistake we say "it must have been a barbie day" and laugh!! At least she doesn't fire me!!!
Did you try a system restore? If you are running widows xp or later you can go to accessories system tools, system restore, your computer will have created a restore point for when you put firefox on. Then you run the restore, it takes a few minutes. It will be back to how you had it before firefox went on.