I recently switched my email client from Mozilla Thunderbird 2.x to Mozilla SeaMonkey (latest) as Mozilla Thunderbird 3.x is so undesirable. Things were working quite well. I found the place to set which component of SeaMonkey it opens to on start up and selected the Mail component.
However there was one annoyance! In Firefox when a web page has a mailto: link, clicking that link would not open a new SeaMonkey email window... I would only see the SeaMonkey program flash in the lower panel within Ubuntu Gnome desktop.
My good friend Daniel who is responsible for the UbuntuZilla project gets the prize for the correct solution. It seems that Gnome in Ubuntu was guessing wrong about the correct switches to launch SeaMonkey with and have it open a new message window. The correct syntax to enter into the Gnome Preferred Applications applet is as follows: