Steps to reproduce: 1. In the address bar, type 'foopy:'. Result: A dialog that says "Firefox doesn't know how to open this address, because the protocol (foopy) isn't associated with any program." and has only an OK button. Expected: Something that also gives me a "Choose an application" button and "Remember my choice" checkbox, like the dialog that appears for "irc:". I'm more likely to need to choose an application when none is registered, yet that's the only time when Firefox doesn't give me the opportunity to do so!
Same issue here, it is really weird how Firefox does not give you the choice of application when no app is registered for the protocol, but actually does give you the choice when you already have one registered. It should simply show the same dialog where you can chose in both cases. It would also be helpful when Firefox would display the full URL that caused the issue instead of only the protocol name, thus allowing for example copy&paste into an application manually that supports the protocol without registering it with Firefox.