An app that allows you to run Firefox 2 and 3.
From the description at CNET:
MultiFireFox is a launcher app that runs both the stable Firefox 2 and the beta version of Firefox 3 at the same time. Copy it and the included Firefox3.app file to your Apps folder.
Looks like the author doesn’t have a project website. If you found it, please let me know. This app is not even listed at MacUpdate.