After installing mono, launchers shown as .desktop

[Guy Rouillier <guyr-ml1 burntmail com>]

I installed mono yesterday on Gentoo AMD64 running kernel 2.6.11-r6.
The OS reports I am running  gnome core 2.8.3.  I'm able to use mcs and
mono successfully.

However, when I rebooted today, all my desktop launchers now have a
.desktop extension (e.g., Thunderbird.desktop), and are apparently being
interpreted as text files instead of launchers.  If I right click and
select Properties, Type is "plain text document", and the launcher tab
is not present.

I don't know why this happened, but how can I get gnome to interpret
these as launchers again?  The apps themselves still work fine if I
start them from either a terminal or the menus.  Thanks.

-- 
Guy Rouillier