Small problem with Firefox vs. Vista's User Account Control. This is not really a bug but I still think Firefox could design around it. Firefox is probably not the only application that might have to worry about this.
So - you're running Vista as a regular, non-admin user.
You go to install Firefox. You're prompted to provide an administrator's credentials. You do.
Now the Firefox installation process is executing in the admin account's context. All good so far. Then the installation finishes, the dialog boxays "installation complete!" and presents a "Finish" button to click. But there's that little checkbox - launch Firefox. If that checkbox is checked, and you click Finish, Firefox will indeed launch and run just fine - as a process in the admin account's context. Which means that everything you do that gets stored in your Firefox user profile - or if you download files to the default location of the desktop - it is actually going into the admin account's profile, or the files are going onto the admin account's desktop - not your desktop!
So, just don't launch Firefox right away after installing it as an admin user. Just close out the installer, then launch Firefox the old-fashioned way: by clicking on its icon.
If I had the time, I'd make this a clearer explanation. If this doesn't make any sense to you, don't worry about it.
So - if Firefox wanted to design around it (really we're talking about modifying the installer, not the underlying app) maybe work out how to have the installer not launch the first run of Firefox using the admin account context but rather go back to the original user account.
Or - hey, wait, why does Firefox need admin rights to install in the first place? Shouldn't it just be able to install as a user-land app? (Or do I have Vista confused with *nix again?)
If I wasn't so lazy, I'd uninstall Firefox then try reinstalling it again without providing admin rights, just to see what would happen. Or I'd google for it.
But nah, I'm done now. Elbow and send....