A better solution is to use the Mozilla Network Security Services (NSS). NSS is everywhere mozilla is and is much more mature.
Yes, that's another approach. Gaim did this though and then implemented support for GnuTLS as well, because having a chat program depend on a web browser was a bit odd and people were prone to go "Ooh look, a new Mozilla is out! rpm -e mozilla, tar xzvf mozilla-1.7.tar.gz" and such, and then their IM client mysteriously no longer connects to MSN.
I think it's better to depend on an actual library, as opposed to a component of another application. Maybe if Mozilla split it out into a separate project with separate releases, packaging etc, it might be better. Maybe they already have ...