@Vivian, no, I did not lose any bookmarks or passwords and have done this twice now. It is probably an add-on causing this, and I think this will get rid of add-ons. It got rid of things like SweetIM Toolbar, etc., but all these you can get back if you want.
I was getting adds popping up on my FAA screen and underlined links leading to adds in text on FAA even in messages like this.
I did not lose anything that I needed.
A computer friend of mine once suggested to try to avoid add-ons as they often created problems.
Sorry I am not explaining this all that well.
It does send a back-up file which I have not needed.
You could initially try what Beth suggested, but if all else fails, try this. Best thing I ever did!
PS After typing this the first time, I went to submit and got the dreaded red screen! so my message was half deleted (I had saved the first half)!!