I found the 1024 firmware for my new PN51D8000 and installed it (via the network, not USB). TV reports firmware as 1024 but not 1024.3 which is current version shown at link below.
It did not install or enable Amazon Prime video support (neither could I find it in the Yahoo widgets). I tried downloading the firmware from the website to a USB stick, but the TV would not find the update.
Interestingly, the information for the 1024 firmware DOES mention something about Amazon, but I think the Google translate of Korean to English garbled things a bit.
The firmware for PN51D8000 is here: http://www.samsung.com/us/support/downloads/plasma-tv/PN51D8000FFXZA
The specific language I refer to regarding Amazon is: "- This firmware can be available Amazon app."
Entire text of what the firmware is supposed to do is:
1. Title Firmware for PDP TV D8000 series.(ver 1024.3)
2. Applicable Model 51D8000FF, 59D8000FF, 64D8000FF
3. Carrier or Corporate Customer all customers
4. Description - This firmware enhances security. - This firmware can be available Amazon app. - This firmware will decrease flickering problem on 3D mode. (only 3D model) - Change the way to get out of Store Demo Mode - Change the type of information of Info banner - Prevent escaping issue when pressing volume button on video apps(Netflix, Vudu, etc) - Support Remote Service - Support Netflix 3.1