First, confirm that your account is an Admin account - in the Apple menu, choose System Preferences, then Accounts. Yours should say "Admin", as opposed to "Standard". If your account isn't an Admin account, you'll need to ask whoever has an Admin account to either install Firefox, or to give your account Admin status. If it is, I would suggest that you Repair Permissions on your Mac, either by booting from the gray DVD that came with it, and choosing Disk Utility from the menu bar, or by using the free tool OnyX .

If you get an error message that you do not have sufficient permissions to update then easiest is to trash the currently installed version to do a clean install of the new version.

• Download a new copy of the Firefox program and save the DMG file to the desktop
• Firefox 4.0.x: http://www.mozilla.com/en-US/firefox/all.html
• Firefox 3.6.x: http://www.mozilla.com/en-US/firefox/all-older.html
• Trash the current Firefox application to do a clean (re-)install
• Install the new version that you have downloaded

Your profile data is stored elsewhere in the Firefox Profile Folder, so you won't lose your bookmarks and other personal data.

Thanks for the quick response. I opened the account under system preferences and see that I am the listed administrator for this account. Since that is so, does this mean that the repairing permissions you wrote about is needed or is there another step I must do before that?

Thank you both very much. The deleting of my older version cleared the problem and I am now operating on version 4. I appreciate the prompt assistance.