More recently, I gave up on using Firefox 3 on a G5. I think it really expects a dual core CPU; it's dog slow on a single core machine. I use it on my MacBook, but on my G5 iMac I use Camino.
There are some page issues -- especially with Google's more obscure applications (Page Creator). Some sites serve up 2nd rate pages because they don't recognize the browser; in most cases Camino would do fine with their Firefox stuff.
Mostly, though it's been great. Since it's a Cocoa app you get OS X services, classy looks, use of the system dictionary, use of the Keychain etc.
Now we have Camino 1.6 with some great features. Among them are excellent AppleScript support and feed detection (but, happily, not a feed reader)
There's only one little glitch with 1.6. Sometimes Camino windows get "stuck" to a (Spaces) Space. I can't easily move them to new "Spaces" the way I do my Firefox windows. It's inconsistent, but annoying. Since it's erratic I assume it's a bug, not a misguided feature. Mostly I can move the windows.
I'm sure it will be fixed soon.
Camino is a great piece of open source software.
Update: It's supposed to work with Google Reader, but danged if I can make it work using the Feed Reader preferences setting! There's zero documentation other than the mention of the feature, and I found nothing in my web searches.
Update 12/4/08: See comments for a recommendation about optimized builds and this terrific site. I'm still trying to figure out how we're supposed to be able to subscribe to a feed using Google Reader!