Debian Mozilla (Wheezy)

• Add to /etc/apt/sources.list next line

  deb http://mozilla.debian.net/ wheezy-backports iceweasel-release
  

• Download pkg-mozilla-archive-keyring
  
• Install deb-package

  sudo dpkg -i pkg-mozilla-archive-keyring*

• Update repos & install newest Iceweasel:

  sudo apt-get update
  sudo apt-get install -t wheezy-backports iceweasel
  

debian-multimedia repo: GPG error

# apt-get update 
...
...
...
 W: GPG error: http://www.deb-multimedia.org testing InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 07DC563D1F41B907

Solution:

 apt-get install deb-multimedia-keyring