All current Macs - iBooks, Powerbooks, G5s,. the Mac Mini, the iMac, or the eMac, all run the full Mac OS 10.3, aka Panther.
There's a version of Firefox for Mac - but the reasons for *needing* Firefox doesn't exist on the Mac OS - they are'nt vulnerable to malware, viruses, trojans, pop-ups, spyware, whatever is lurking out there. The Safari web browser which is free with the Mac OS is very similar to Firefox, and has tabs and a built-in pop-up blocker, and will probably suit you just fine.
I run firefox on my Macs, it is noticeably faster than Safai and it has support for RSS feeds to be tracked as bookmarks, something Safari won't have until Tiger ships from what I've heard.
The computer is running IExplorer 5 right now, which lets in popups...it has another browser, Safari, installed that I can switch to?
Thanks. Sorry for the ignorance, am used to Windows.