I wouldn't want Firefox on any Amiga, it runs like shit stuck in tar on this 1.7Ghz Linux PC. But if you want it for AmigaOS, as well as all that other boring Linux software, start porting to AROS. Hyperion have made it clear that they are NOT going to port AmigaOS to x86 (although I don't think they've specifically excluded x64). If you think PPC is dead in the water, then MorphOS and AmigaOS aren't going to offer you what you want any time soon.
AROS and Anubis on the other hand are making steady progress, and encourage developers to contribute directly towards bettering the OS and shaping it the way the USERS want, not some faceless head company. AROS already has a web browser capable of visiting and rendering most websites perfectly, it's called Origyn Web Browser and it's already got Flash support working in some builds, thanks to Gnash.
You can also buy a PC with AROS peinstalled and setup, it's called the iMica. You can order one here, and they're certainly cheaper and more powerful than a Sam - http://www.clusteruk.com/