|It seems after many months of "mailto: is not a registered protocol" I've finally managed to beat Mozilla [Linux] into submission and get it to open Scribe to send an email.
This 'wizardry' was accomplished with MozEx, an extension for Mozilla (why it's an extension and not PART of the application I don't know). Anyway, with a non-user friendly command like:
/.../Scribe/scribe -m "%a" -c "%c" -s "%s"
MozEx will pass all the parameters of the mailto: link down to Scribe, where with some newly written shared memory black magic it passes the arguments to the running instance of Scribe and up comes the compose window with all the arguments in the right place.