this might help...
http://discussions.europe.nokia.com/...re/td-p/604648

Try the following commands:
sudo gainroot
gpg --keyserver pgpkeys.mit.edu --recv-key 667387BFFF445C24
gpg -a --export 667387BFFF445C24 | apt-key add
- until the final "OK" display on your screen. Good luck！
as mentioned in the below blog
http://support.mozilla.com/en-US/questions/805722