@Defiant re: FF vs. IE vs. Opera
Sorry, man, but I just can't get behind that. As other commenters here have asked -- show me your test results. Huh, didn't think so.
I still keep a copy of the last version of IE released for MacOS -- v5.2.3 -- around, for those few sites left out there that insist on doing historical re-enactments of the late '90s ("this site works best with Internet Explorer"). I haven't touched it in nearly five years.
I ran screaming from IE as soon as the first stable version of the original Mozilla browser appeared (pre-FF), and haven't gone back. In fact, I still keep a copy of the most recent version of Mozilla (before they went to FF) around on both my G4 tower and my G4 iBook for those rare occasions where FF has issues with a site. What the hell; it's old, but it's good.
I tried Opera once -- admittedly, back in the old ad-supported freeware days -- and it ran like a goddamn' glacier, that is, slow and freezing. I haven't bothered with it since.
I gave Safari a quick try when I first got my G4 tower with OSX pre-installed, and quickly dumped it after discovering its inability to import bookmarks from other browsers (what were they thinking?).
That brings me to Firefox. As I mentioned in a couple of other discussions, I'm still sticking with 126.96.36.199 because 3.x ran unacceptably slow, not to mention that I couldn't shut off the site icons that loaded next to site names in the Bookmarks menu, and which slowed FF waaa-aaay down, to the point where I could actually watch the menu popdown being drawn on the screen -- that is, when it didn't cause Firefox 3.x to do its Challenger imitation (kaboom, crash). Btw, FF _still_ doesn't give me a Preference that allows me to turn the damn' icons off in the Bookmarks menu so that FF runs at something resembling acceptable speed. FF 2.x also has the thumbnail icons in the Bookmarks menu, but somehow doesn't have the same slow-loading/crashing issue that 3.x does. I know I'm not the only one having this problem, and I wish to hell they'd frickin' _fix_ it, already.
As far as being optimized for any particular OS, I can say from my own experience that Firefox -- up to 188.8.131.52, at least -- runs quite snappily on both of my G4 systems, especially with the judicious use of NoScript and FlashBlock.