Why is Firefox slow?

[Tomisimo]

I've been using Firefox (http://www.mozilla.com/en-US/firefox/) for a couple of years and I love it. But lately it's been getting really slow and takes a long time to open for some reason and I can't figure it out.

Has anyone else had this problem before?

[WMX]

I had that problem once and I had to delete a file in the mozilla directory in program files, I can't remember what file it was but it ended in rdf.