The attached patch allows the Usermin mailbox module to be used for mailto: links in web pages using Firefox3. See http://developer.mozilla.org/en/docs/Web-based_protocol_handlers for details of how this works.
The main change is to mailbox/reply_mail.cgi to allow this to respond to mailto: links by creating a new message populated with To:, Cc:, Bcc, Subject and mail body specified in the link. This requires that the user is already logged in to Usermin and the "Trust links from unknown referrers" option is enabled in Usermin config.
To use this feature from Firefox3, the mailto: handler must be registered in the browser. This patch adds an installer page attched to the "Help" menu of the Mailbox module. Follow the "Help" link from the mail list screen to install.
Patch built against usermin-1.350.tar.gz