Comment 46 for bug 411358

I think this is all a bit dependent on the version of GNOME is in use. I am running Ubuntu 10.04 LTS which still uses GNOME 2.30.2

Looking at the git master for GVFS the latest code no longer appears to have any reliance on gconf. I guess that the GIO implementation in GNOME 2.30.2 is somewhat transitional.
I've just installed Ubuntu 12.04 + GNOME3 (gnome-shell) in a virtual machine and can confirm that thunderbird (versions 11.0 and 14.0) does not encounter any GConf errors running under GNOME3.

This all poses a slightly tricky question... Who's fault is this and who should fix it? Honestly, I don't know enough about the history of Thunderbird and GNOME to be sure, but the GNOME team possibly shot themselves in the foot a bit by choosing GConf as the central URI -> Application mapping database when it cannot fully support RFC2396 URIs. But then this seems to have always been the case and so with this known limitation, there seems to be little point in querying potential URIs which will fail to resolve.
Using GConf natively does not really cause a problem as the messages only go to stdout. The annoying pop-ups only occur when GNOME 2.x versions of GIO are in use, but I don't know if there's any easy way for thunderbird to test which version of GIO being used and change its behaviour based on that.

In my opinion, the essence of the plain text URI parsing in Thunderbird is primarily for making clickable links for http:, https:, ftp:, mailto:, etc... For these purposes it seems unnecessary to check the full extent of the scheme defined in RFC2395. As there are currently no known URI Schemes which use any non alphanumeric characters (see http://en.wikipedia.org/wiki/URI_scheme ) I thinks there is an argument to suggest that the regular expression used to determine what might be a URI, could be changed so that '+' isn't considered valid.