Rated 2 out of 5 stars
I second Sandman comments.
Why not simply make the URL look like a link that I can simply double click upon?
I can't find a add-on that does this with TB 3.1 sadly.
No re-writing of the email
Because (a) it's nowhere near simple (it requires some complicated rewiring of the email's DOM - I have looked into it), and (b) I *really* prefer to see emails as they are, not with extensions having quietly re-written bits of them.
Bit mean to mark /me/ down because you can't find an extension that does exactly what /you/ want ...