Mozilla says it’s unlikely that the final version of Firefox 4 will run on older Macs with PowerPC processors, according to “Computerworld” (http://macosg.me/2/sf). Apparently, you’ll need a Mac with an Intel processor.
“We are not likely to be supporting PowerPC,” said Mike Beltzner, director of Firefox, in a message Tuesday on the Mozilla.dev.planning discussion group. “[But] no announcement has been made yet, as I’d like to have the data to back it up, and am having trouble getting it.”