I just imported a CA certificate (the Fedora project's certificate). Firefox asked me what I want to trust that certificate for. The questions are unclear. Choice 1: Trust it to identify websites? This one makes sens. Choice 2: Trust it to identify email users? What the *!&@ does that mean? This is Firefox, not Thunderbird. Choice 3: Trust it to identify software developers? Seriously? Does this mean that I would trust this CA to grant privilege to people's software? Does this mean that I would trust this CA to tell me who wrote Firefox add-ons? Why are you asking me this question? (I'm not saying that #2 and #3 shouldn't be there. I'm saying that the descriptions could be a lot clearer.) I suspect that these are actually related to X.509 constraints. These constraints are, alas, *completely irrelevant* to a web browser, as far as I know. CAs are either allowed to sign HTTPS certificates (or intermediate CAs) or they are not. That should be all.
Thanks for filing the bug. The UI in question is shared by Firefox, Thunderbird etc, which is why stuff like e-mail trust shows up even in Firefox.