I would be curious to know if you got the same problem using the portable version of firefox. (
www.portableapps.com).
I have firefox and IE at home and never had a problem but I am starting to get into the portable firefox as you can carry it about on your usb stick and it means that your web browser, extensions and shortcuts are always there no matter what machine you are on.
One problem is I can easily spend hours with the stumble upon extension - when you install it you pick your favourite topics then when you click your stumble button on the toolbar it picks a site with that topic from the net. You get to see pages you would never have looked for but on topics you are interested in. If you really like the page give it a thumbs up, if you hate it a thumbs down and if you cant be bothered just click the stumble button and move on.