Firefox 3.5: Firefox doesn't know how to open this address, because the protocol (foo) isn't associated with any program.

Humph. I'm not having any success creating a new protocol that maps to an external application in Firefox. I have these in my prefs.js:

user_pref("network.protocol-handler.app.foo",
  "/Applications/TextEdit.app/Contents/MacOS/TextEdit");
user_pref("network.protocol-handler.expose.foo", true);
user_pref("network.protocol-handler.external.foo", true);
user_pref("network.protocol-handler.warn-external.foo", false);

Have you got it working?

I've seen these: knowledge base entry, registering a protocol, and path not found error. This one I didn't get to the bottom of: whitelisting protocols.

Here's my about:config which shows my default settings as well:



Edit: this is supposed to fix the problem:
"protocol-handler.expose. is required to be False and then when click on link of this type one will be asked for application to handle it. It's important not to type :// in address bar but click on link of that type or you'll get the same error. Then your protocol will appear in Edit->Preferences->Applications." [more]