Various readers have found an incompatibility between iWeb and Firefox 3. We let the words of Keaps say it all:
I have just raised a problem with Firefox 3 and iWeb when you publish a site with iWeb, the photographs are invisible on Firefox 3 with Firefox 2, Safari all is well Not very practical if everyone has updated, since this will show web sites without contents! :-( While waiting for a official solution, a work-around is available.
It is available as a script that can be downloaded from the following address:
http://www.macupdate.com/info.php/id/27819/fix-iweb-and-firefox-3
[translation by crispin]