The user should be able to import certs from the clipboard. Ideally, the client should first look at the clipboard. If the clipboard contains a valid cert, ask the user if this is the cert s/he wants to import. If not, present UI for picking a file, or to enter an URL (possibly contained in the clipboard, too?). While we already support importing a certificate from a URL within a browser (you simply go to the URL and the content will get imported), this approach is not possible in applications like Thunderbird, who do not use a browser window.
reassign bug owner. mass-update-kaie-20120918
This would probably be best as an add-on.