Thibault himself asked the same question a long while back:
http://www.geocrawler.com/mail/thread.php3?subject=K-Meleon+GPL+license&list=111
One of the answers is really interesting: 'You know having to deal with this is really kinda stupid in an "open source" development forum. We`re not any better than Micros***.'
Anyway, I think I've read somewhere that Mozilla is working to make a GPL-compatible license now that GPL is very widely-used.
At this time, probably we are violating a license, but people doesn't seem to care since everyone's happy.