The latest 9.0.x version is not compatible with your os.

see : Firefox 9 System Requirements

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 3.6.25 , your can download from here:

http://www.mozilla.org/en-US/firefox/all-older.html

see : Firefox 3.6 System Requirements

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

(For the record) See:

• Firefox 3.6 is no longer supported
• Firefox no longer works with Mac OS X 10.4 or PowerPC processors

Not mentioned in the articles is the fact that there's a third-party build of Firefox that is kept up-to-date. Ideally, you should upgrade your operating system if possible. But if you can't, then TenFourFox is a better option than using an obsolete version of Firefox that contains security vulnerabilities.

• www.floodgap.com/software/tenfourfox/

TenFourFox used to be mentioned in Firefox won't start - find solutions in this revision for mac: https://support.mozilla.org/en-US/kb/Firefox-not-start/revision/22114 before the latest revision that removed it, to link to the new article:

{for mac} Firefox will not start on OS X 10.4 or earlier or with a PowerPC processor

Mozilla has stopped supporting OS X 10.4 and earlier, and also OS X 10.5 with a PowerPC processor. None of these operating systems or architecture are supported by Apple (and have not been for quite some time) and have multiple vulnerabilities that will remain unpatched. As such, you have the following options listed from the most to the least secure:

• If you have an Intel processor you can update to OS X 10.6 or 10.7. This is the most secure option. If you don't want to pay for a new operating system, or if you have a PowerPC processor you can install a Linux distribution. This ensures you have a completely secure system and access to all the great new features in Firefox.
• On OS X 10.4 or 10.5 with a PowerPC processor, you can download a fork of the latest Firefox version designed only for PowerPC from the TenForFour home page.{note}Note: TenForFour is not affiliated with nor supported by Mozilla in any way, and is not an official build.{/note}
  • You can also continue to use Firefox 3.6 which you can download from this page. {warning}Warning: Firefox 3.6 will only be maintained with security and stability updates for a short period of time.{/warning}
• On OS X 10.3 and earlier, you can continue to use Firefox 2.0.0.20. Just because the browser will no longer receive security updates doesn't mean it will simply stop working.{warning}Warning: You will be using unsupported software on an unsupported operating system which poses a significant security risk.{/warning}

{/for}

P.S. I started a new discussion thread here, asking to add that information:

• https://support.mozilla.org/en-US/kb/firefox-no-longer-works-mac-os-x-104-or-powerpc-pr/discuss/2403 Include information on TenFourFox?

In https://support.mozilla.org/en-US/kb/firefox-no-longer-works-mac-os-x-104-or-powerpc-pr/discuss/2403 Include information on TenFourFox?

scoobidiver said
Although it's safer to use the latest version of TenForFour than Firefox 3.6.28, users won't use it because it doesn't support plugins from version 6. So I don't think it's worth mentioning it.

P.S. Michael Verdi updated Firefox no longer works with Mac OS X 10.4 or PowerPC processors on May 3, to mention TenFourFox.