Firefox Troubles

A few months ago, Firefox stopped displaying graphics properly. It won't show backgrounds or certain page elements, like buttons. Most of the time it's no big deal (which is why I put up with it so long) but sometimes it is - for example if I'm filling out a form, I might have to guess at where the "submit" button might be. Try to find a spot where the arrow turns to a pointing hand, or hit "enter" and hope that works.

I don't think about what I'm missing most of the time until I happen to see a familiar site on another computer, or get fed up and use MSIE instead. Which I don't like because I enjoy Firefox's plugins.

I don't know what I did, if I did anything - could I have accidentally clicked a setting? I even upgraded Firefox to the most recent version but it's still the same.

Any clues?

I cannot use the 'submit' button on Restaurant.com to enter discount codes. I have to go to MSIE. I think that it's a Firefox issue.