Firefox 4 versions and later '''do not run on a PowerPC''' Mac and require '''at least OS X 10.5 and an Intel Mac.''' '''The latest supported version for your os is 3.6.26''' , you can download from: http://www.mozilla.org/en-US/firefox/all-older.html see for more info: [http://www.mozilla.org/en-US/firefox/3.6/system-requirements/ Firefox 3.6 System Requirements] [http://www.mozilla.org/en-US/firefox/10.0/system-requirements/ Firefox 10 System Requirements] see also : [https://support.mozilla.org/en-US/kb/Installing%20Firefox%20on%20Mac Installing Firefox on Mac] [For older Macs that aren't supported in Firefox 4+ versions, if you like, try TenFourFox for PowerPC's running Mac 10.4.11 & 10.5.8] http://www.floodgap.com/software/tenfourfox/ http://tenfourfox.blogspot.com/ https://code.google.com/p/tenfourfox/wiki/PluginsNoLongerSupported thank you Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.