The header is defined in RFC 2369 which I wrote with Grant Neufeld back in college.

dating mailto-80

I realize that Firefox itself won't handle e-mail.

What I neglected to include was the fact that I am a gmail user, and want to use Firefox as a way to handle Mailto links.

And get rid of the space the forum puts in between the ? Although if you're using JSP you might want to look at its server-side email capabilities as an alternative to using "mailto".

The List-Unsubscribe header is an optional chunk of text that email publishers and marketers can include in the header portion of the messages they send.

I'd like to use Firefox to open Mailto links in Windows 8.

I found this support article, but it isn't relevant to Windows 8:

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* If network.protocol-handler.external.mailto prefs are user set (bold) then right-click and Reset them to the default value. However this does not seem to help me if I click on a Mailto link OUTSIDE of Firefox (say, in another browser or in a contact management database I use).

When I do that, the awful Windows 8 Metro-based Mail app takes over my screen.

Sorry if my question wasn't clear from the beginning, and thanks again for sticking through this with me!