There may be some platform-specific code that needs to be written to get the list of apps that is registered to handle a MIME-type or a content-type locally so that they can be offered as options to the user. beltzner, faaborg: should we be shooting to list all apps that are registered as knowing how to handle a specific content type, or just the default?

The basics of this code already exist and are in the tree, which is to say that we can get at least one handler for a given protocol or MIME-type on any platform if it exists. I assert this is sufficient for Firefox3. Windows is improving its support for more apps in the MIME-type case in bug 348808. I suspect that at some point, the Mac and Linux code could be changed to do something similar, and probably want to be updated to newer system-level APIs.

This doesn't actually block Bug 372441

Bug 400852 covers this for windows, and there are other bugs open for application picker support on other platforms.