I have just found out that they plan to drop support for Win9x/ME in Gecko 1.9
At the moment the current Firefox build is using Gecko 1.8.x but the plan is for Firefox 3 to change over to Gecko 1.9 and so taking effect in a few years time, when Firefox 3 comes out, there will be no support for Win9x/ME, although if enough people want it, and some programmers volunteer to take on the responsiblity, there might be a community maintained distribution of Firefox 3 which does support Win9x/Me but only time will tell.
As far as I understand it, the upcoming Firefox 2 will still support Win9x/Me. It looks unlikely that they would remove Win9x/ME support now for Firefox 2. Get firefox from http://www.getfirefox.com
It's fast, stable, secure, functional, internet works pretty good!
Does not "suport" any viruses ( there might be a few, but are destructable only to older kernel versions )...