Originally Posted by thelonius
what does it mean ? I didn't get this message for the same package (mozilla) before.
You have upgraded apt/aptitude to the testing or unstable branch and it uses gpg to verify the packages. If you want to get rid of these messages then you should do a search on using secure apt
and as root import the keys into the root keyring then use the apt-key add
to add the key to the apt keyring.
Edit: Installing the package debian-keyring can help get rid of the messages as well.