MisFox helps you access several Internet settings which were available under Mac OS 8 and 9 and are still present -- but hidden -- in OS X. So if these settings gets corrupt for some reason there's no way to repair these settings anymore. MisFox makes some of the most important Internet settings accessible again.
MisFox will show all the file mappings settings and the protocol helpers. You can inspect these settings, but you can also edit, delete and create new items for these settings.
The File Mappings are used for many tasks. First they will translate the "content-type" and file extensions which are used in the Internet into the file type and creator codes which are used on the Mac. Second they do define what to do with files of a certain file type after they are downloaded from the Internet (for example they define that ".sit" files should be processed by Stuffit Expander). Protocol Helpers are used to find the right application to handle certain Internet protocols. So a Web browser will use the protcol helper settings to find a news reader when clicking on a "news:" link in order to open this link. Since Mac OS X 10.2 there's no way to define the default news reader in the system settings anymore. So you can do this in MisFox now.