Gallery images do not show up for some users

Installed Firefox 3.0 on 3 Macs:
Intel MacBook running 10.4.11 (Tiger)
G5 iMac running 10.4.11 (Tiger)
MacBook Air running 10.5.4 (Leopard)
I have an install of GALLERY on my website that works fine in every browser EXCEPT Firefox 3.0 on the Macs running 10.4.11 (Tiger)
The Gallery images/thumbnails load fine in every other type of browser on those machines and worked fine in Firefox 2, but once 3.0 was installed the images do not load.
the url of the GALLERY is:
it does not matter if www is there or not, the result is the same when using the Macs with 10.4.11 (Tiger)
Is this an OS issue?
A Firefox 3.0 issue?
A Gallery install / webhost issue?
How can I troubleshoot this to determine where the issue is?

I also just got an email from someone today saying they had the same problem viewing any images at that URL but they were on XP and Netscape, Firefox and IE refused to load any images.

Gallery version = 2.1 core 1.1.0
PHP version = 4.4.8 cgi

I don’t have Tiger handy, so I can’t test this. What I would do is:

  1. Load a gallery page in Firefox 3.0 in Tiger
  2. View Page Source, or Save As Web Page, HTML Only
  3. Load same page in Firefox 3.0 in Leopard
  4. View Page Source, or Save As Web Page, HTML Only
  5. Compare the source code from both views. BBEdit can do this, as can the ‘diff’ command in Terminal

One can also right-click on the (missing) image to see its source. Gallery does some magic since images aren’t usually hosted in a web-accessible directory.

Another consideration is if URL-Rewrite is enabled. Is it? And if so, which method? .htaccess (mod_rewrite) or the PHP rewrite?