I downloaded Firefox 4.0 and It will not run on Mac OSX 10.5.8, on a Mac G5 dual 2.0ghz. Now my older version of Firefox is gone...Why won't it work, the download page says it is for OSX and does not say it will not work on any particular OSX. Can your clarify. And can I get the old Firefox 3 back or should I continue using Safari....?