So, what is happening here is that the mimetype of the attachment is application/x-debian-package, which isn't a registered mimetype according to glib. In this case, FIrefox is meant to fallback to looking up via extension type (and it does correctly map the .deb extension to application/x-deb, which is a registered mimetype), but the fallback case is totally broken
** Summary changed: - Architecture-independent .DEB packages (_all.deb) not connected to software-center + Default handler lookup by extension fails -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/760644 Title: Default handler lookup by extension fails -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs