If you add Mozilla repository  in debian Testing (mozilla.debian.net) it can happen that when we try to execute the comand apt-get update, we see a GPG error:

W: GPG error: http://mozilla.debian.net experimental Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 85A3D26506C4AE2A

To solve this problem we need to install the debian-keyring package

# apt-get install debian-keyring

and then execute this 2 commands:

# gpg --keyserver keys.gnupg.net --recv-key 06C4AE2A

# gpg -a --export 06C4AE2A | apt-key add -

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