when I opened Firefox, it said I needed to update for higher security. I downloaded the newest version for my Mac and when I open Firefox now, it says ' you can't use the application Firefox with this version of Mac OS X.How do I get the old version back?

I have Mac OS X version 10.4.11. I was prompted to update and download a higher security version of Firefox because the one I was currently using was not secure enough. I updated it, and now when I try to open Firefox it will not let me use it and says ' you cannot use the application Firefox with this version of Mac OS X.' I want the old version of Firefox back, how do I get it??