Tell that to websites that specifically check for firefox on windows, otherwise don't let you in (yes, I saw plenty of those, and if you delve into the javascript to pass after the gatekeeping page, unsurprisingly everything works as expected).
Not to mention sites using activex (those I'd avoid even if I were using IE) or requiring a specific version of flash, quicktime or other crap like that.

Where did I say that it fits everybody's needs? I just said that I want to use it without some ***** imposing me some windows only technology. That's partially acceptable for private enterprises (after all they're losing a potential customer) but it's totally unacceptable for public institutions.