I’ve been checking out Firefox 3 Beta 5 since it’s the default browser in Kubuntu 8.04 Hardy Heron. When I went to Preferences and looked in the Applications section to fix the action for the file content type, it was empty. That’s not good.
If you’re running into the same problem, there’s a very easy fix for it. Open your favorite package manager (Adept is the default one for Kubuntu) and install the firefox-gnome-support package. A few other support packages will be installed to resolve dependencies. Then, restart Firefox and all will be well.