I'm running Fedora 17 with the KDE desktop. KDE's system settings ("control panel") claims the default mailto application is Kmail. And, since Gnome is still present, I see that it thinks the default mailto application is Evolution. I don't see anything in /etc/alternatives that seems relevant to a mailto handler. Firefox says, "Firefox normally uses your operating system's default mail program to send an e-mail message." <http://support.mozilla.org/en-US/kb/change-program-used-open-email-links>) But Firefox says the default handler is Thunderbird. Where the hell is Firefox finding that value? And Firefox doesn't offer either of the other two "defaults", Kmail or Evolution, as options (except through the "other program" mechanism). Can anyone explain what's going on? I'd like to change the mailto handler. But I need to pass some arguments to my program and Firefox doesn't offer that ability itself. To get that ability, I need to be able to change the system default so that Firefox recognizes the change. But where is Firefox finding the "default"?