Debian – Where to download Chrome 32bit

You can use /etc/apt/preferences to specify which versions you want on a per-package basis.

To have the latest iceweasel version, use (at your own risk) the following configuration files:

/etc/apt/preferences

Package: iceweasel
Pin: release a=experimental
Pin-Priority: 1000

Package: *
Pin: release a=testing
Pin-Priority: 500

Package: *
Pin: release a=unstable
Pin-Priority: 400

Package: *
Pin: release a=experimental
Pin-Priority: 300

/etc/apt/source.list

deb http://http.debian.net/debian testing         main contrib non-free
deb http://security.debian.org/   testing/updates main
deb http://http.debian.net/debian unstable        main contrib non-free
deb http://http.debian.net/debian experimental    main contrib

But beware the the apt_preferences(5) manpage warns

Packages included in a specific release aren't tested in (and therefore don't always work as expected in) older or newer releases, or together with other packages from different releases. You have been warned.

First of all, despite the last line start with E: (which indicates an error), apt didn't fail entirely; it's downloaded most of the updated package lists, it only skipped those for Opera and the Google Talk plugin. So apt upgrade should still offer to upgrade all the other packages.

The warnings give you some indication of what went wrong:

W: gpgv:/var/lib/apt/lists/dl.google.com_linux_talkplugin_deb_dists_stable_Release.gpg: The repository is insufficiently signed by key 4CCA1EAF950CEE4AB83976DCA040830F7FAC5991 (weak digest)
W: gpgv:/var/lib/apt/lists/deb.opera.com_opera_dists_stable_InRelease: The repository is insufficiently signed by key 419D0ACF314E8E993F7F92E563F7D4AFF6D61D45 (weak digest)
W: Failed to fetch http://dl.google.com/linux/talkplugin/deb/dists/stable/Release  No Hash entry in Release file /var/lib/apt/lists/dl.google.com_linux_talkplugin_deb_dists_stable_Release, which is considered strong enough for security purposes

The first two mean that the repository descriptors were signed with an old digest algorithm, which apt now complains about. The third is caused by apt's recent switch to SHA-256 or SHA-512 hashes only; the Talk plugin repository only provides MD5 and SHA-1 hashes, which are now ignored by apt.

To fix this, you can either remove the repositories for the time being, or wait for Opera and Google to fix them...