I have tried this problem, and I confirm that mtypes works correctly, but it's K-Meleon which doesn't verify the mimetypes.rdf parameters before opening. Open seems to only open the default program
I think it's a bug for Dorian.
A+
Mozilla/5.0 (x11; U; Linux x86_64; en-US; rv:1.9.1.17pre) Gecko/20101211 Ubuntu/12.04 (precise) K-Meleon/1.6.0
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:1.9.2.14pre) Gecko/20101219 Ubuntu/12.04 (precise) K-Meleon/1.7.0
Web:
K-Meleon Extension Setup (French) and
(English)
Web:
http://jujuland.pagesperso-orange.fr/
Mail : alain [dot] aupeix [at] wanadoo [dot] fr