Firefox 1.5.02 working as normal here.
I might suggest that you check Tools>Options>Content>
Perhaps the check box is selected next to "Load images for the originating site only"??
Just a guess.
BTW I've have weird, weird FireFox displays lately. Mostly wrong ICONS in the wrong places. I've cleared my cache. Ran FF in safe mode. (Which you might want to try to see if an extension is hosing up things.) And finally completely un-installed and re-installed, still no joy. Never have figured out what is going on???
Good luck.