https://support.mozilla.org/en-US/kb/firefox-no-longer-works-mac-os-x-10-5

Firefox 17.0 to the current 48.0 has required OSX 10.6 at minimum to run.

Note Firefox 49.0 will require OSX 10.9 at minimum to run. https://support.mozilla.org/en-US/kb/firefox-osx

Thank you for the reply. My problem is i have to stay on 10.5 in order to run certain programs. Any earlier version ?

The newest version you can run on a Intel Mac with OSX 10.5 is Firefox 16.0.2 which you appear to have?

So you want to use a even older and more vulnerable version of Firefox?

https://ftp.mozilla.org/pub/firefox/releases/

Thank you again. I did not know if there was another version that came after that would still work. Looks like that is not the case. Really appreciate your help. Thanks again.

I did mention this in first reply.

James said

Firefox 17.0 to the current 48.0 has required OSX 10.6 at minimum to run.