When I click an email address in Osmo 2.12 the composer window is opened with the <B>To:</B> field set to <B>file:///</B> followed by the email address. From a command line xdg-mail does the right thing so <B>file:///</B> must be coming from Osmo.
It looks like the default file:// protocol comes from the Webkit webview.
This patch should fix the issue in Contacts.
The patch also fixes the problem with Web urls without a protocol.
E.g. www.google.com causes
xdg-open: file '/www.google.com' does not exist
Thanks for the patch! Applied in r966.
I am running version 0.2.12 under Linux Mint Cinnamon and am still having this same problem. I downloaded the patch referenced above, but don't know how to apply it.