"We believe a Mac OS X 10.5 minimum will allow us to provide the best experience possible to our users," Mozilla Mac programmer Josh Aas said on Tuesday in a mailing list announcement.
Firefox is built on a browser engine called Gecko, and the upcoming version 1.9.3 will have technology for Mac OS X 10.4 and before removed, Aas said.
The recently released Firefox 3.6 works on Mac OS X 10.4, aka Tiger. Mozilla will support it for some months after the browser's replacement version is issued, which means 10.4 support should continue into 2011.
For more on this story, read Next Firefox to drop Mac OS X 10.4 support on CNET News.