What they said, and...
....tenfourfox, auroafox are, still essentially at source parity with Firefox. So you get all the goodness of Firefox and its powerful library of extensions, like Greasemonkey, Adblocker, etc etc...how much longer we will have this, no one knows, not even Cameron Kaiser. But, he and Tobias Netzel (Aurorafox and Leopardwebkit developer) have pulled off some major programming wins in the past, here's to hoping they can continue to do so for a few more years.
No sane PowerPC user should be using plain Jane Safari in 2013. Its old, slow and unsafe. Use Tobias Netzels Leopardwebkit instead, which will give you a faster and more modern webkit engine inside your 5.0.6 Safari. Also, use ClicktoFlash and ClicktoPlugin extensions to dump flash off your PowerPC mac. Flash is also old, slow and unsafe.
I don't sound like a broken record, I am a broken record.