There are various ways you can go about getting a newer Firefox and installing Thunderbird but honestly, I don't think it's worth going to to them. You should either buy a subscription for SLED or stop using it.

SLED is great if you want a stable version of Linux with long term support and are willing to pay for updates. If you are not going to buy a subscription it just isn't sensible to use it. By running SLED without a subscription you're subjecting yourself to all the risks that come with running an OS that never gets updates installed. If you had a subscription you wouldn't have Firefox ESR 17.

If you're not going to buy a subscription for SLED, switch to openSUSE. 13.2 gets released tomorrow.

Regarding GNOME 3, look at the GNOME Classic variant. It gives you the benefits of GNOME 3 without the frustration of there being nothing familiar on the screen. (Last I checked, GNOME Classic isn't installed by default on openSUSE but you can get it by installing the gnome-shell-classic package.) If you really can't get on with GNOME 3 even in Classic, check out XFCE https://en.opensuse.org/Portal:Xfce which is included in the main openSUSE repos. There's also MATE https://en.opensuse.org/Portal:MATE which is a continuation of GNOME 2 but requires adding additional repos.

The openSUSE forums are at http://forums.opensuse.org/ and you can use the same username and password you use to post here to post there. Info about Bumblebee, which I see you've previously asked about is at https://en.opensuse.org/SDB:NVIDIA_Bumblebee