Then the next thing to check would be your Firefox settings.
In a new tab, type "about:config" in the address bar. Then in that search pane, type favicon. Only one options should come up, "browser.chrome.favicons".
If it's true, it should show. If false, it (and all others) won't.
Thats the default icon supplied by our new host. Its a combine 'h' and 'm'; the initials for our new host. Since we don't have an official icon for our site, and it didn't seem to cause any problems, I didn't bother to get rid of it. The other old icon you pointed to was the default from vBulletin, the software we use for the forums.