just downloaded firefox4 and when i try to open it get an error message on mac saying 'you cannot use the application "firefox" with this version of Mac OS X'. what do i do?

Firefox 3 requires at least OS X 10.5, you can get Firefox 3.6 from http://www.mozilla.com/en-US/firefox/all-older.html

thank you for your help. It is appreciated

thanks for help. they should check system before allowing you to replace with something that doesn't work, especially as had taken safari off system, so major pain getting access to net again. but all done now