Firefox 4 doesn't run on a PowerPC Mac. Firefox 4 requires at least OS X 10.5 and an Intel Mac. * http://www.mozilla.com/firefox/4.0/system-requirements/ For Mac OS X 10.4.11 or Mac OS X 10.5.8 you can look at: * http://www.floodgap.com/software/tenfourfox/ Firefox 3.6.x can be found here: * http://www.mozilla.com/firefox/3.6/system-requirements/ * http://www.mozilla.com/en-US/firefox/all-older.html Firefox 2.0.0.20 is the last release that runs on Mac OS X 10.2 and 10.3 * http://www.mozilla.com/firefox/2.0/system-requirements/ * https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/2.0.0.20/mac/en-US/