I had the same problems too, had the same firefox profile since the 1.0 days almost, and had my history set to remember it for 1 year, my profile dir alone was

I had the same problems too, had the same firefox profile since the 1.0 days almost, and had my history set to remember it for 1 year, my profile dir alone was over 2GB. After starting a fresh profile everything went back to pretty much normal (by firefox's standards)