Managing downloads with Firefox 1.5 beta

I haven't seen this mentioned anywhere yet, but upon opening the Downloads pane of the Firefox 1.5 beta preferences, there's a "View & Edit Actions..." button.

This opens up what I would assume is a not-quite-finished feature that appears to allow you to dictate what applications, if any, are used to open specific file types that you download. It seems unfinished as I can't find a way to add new types to this window – yet. I realize this can kind of be accomplished simply by using OS X's Get Info command, but I really hope Mozilla finishes this feature to its full potential, as it adds are serious layer of power to the downloading, opening and installing experience of surfing the internets.

On a bit of a personal note: if anyone out there is skilled at building Safari plugins, I'd be happy to drop a few bucks on something like this for Apple's browser.