Comment 0 for bug 515386

On, it says Moziila Thunderbird does not support email attachments from xdg-email.

It turns out Thunderbird disabled attachments via a mailto: URL on purpose, because they believe it is not secure. [1]

I'm proposing the following workaround: (see attachment)

In open_kde() / open_gnome(), look up the email client kde/gnome is trying to run. If the client contains Thunderbird in its name, then call run_thunderbird(), which parses the mailto url, reformats it in a way that Thunderbird accepts, and then run Thunderbird.

open_xfce() does not need to do this because exo-open already does this. [2]