|In my experience, yes -|
(a) Windows 98/98SE/ME can only run the original release of Internet Explorer 6 (sometimes called Internet Explorer 6 Service Pack 1). The Service Pack 2 release of IE6 requires Windows XP or later.
(b) The latest version of Firefox which will run on Windows 98/98SE/ME is Firefox 18.104.22.168 (Firefox 3 requires Windows XP or later).
However, it is possible - as mentioned - to patch Windows 98/98SE/ME to run programs which require Windows XP, by installing the program KernelEx (the Kernel extender), such as Firefox 3 (as stated above). But also Internet Explorer 7 (I've not yet tried this with IE8.)
KernelEx allows the running of Windows XP applications on Windows 98/ME by using custom API libraries that implement (or simulate) functions and procedures needed by WinXP programs.
It neither requires nor includes system files from other Windows products such as Windows 2000 or Windows XP. The only requirement is that the user first installs the free Microsoft Layer for Unicode (MSLU) from:
Then download KernelEx 4.0 from:
Some instability issues can arise if you omit the first step. I've seen reports of the latest beta release of KernelEx crashing, but the reports don't always make clear whether or not the user had actually omitted that important step.