This is the error I'm getting:

```
W:GPG error: http://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D1106511179518B2, 
W:Failed to fetch gzip:/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_quantal_main_source_Sources
 Hash Sum mismatch
W:Failed to fetch gzip:/var/lib/apt/lists/partial/ppa.launchpad.net_mozillateam_firefox-next_ubuntu_dists_quantal_main_binary-i386_Packages
 Hash Sum mismatch
E:Some index files failed to download. They have been ignored, or old ones used instead.

```

How can I fix this?