Android 4.3 ports are starting to come in, slowly but surely. An Android 4.3 rom, built from source is now available for the first generation KindleFire. Below are the basic requirements for you to try Android 4.3 on your first generation Kindle Fire:-
- Should be running FireFireFire Bootloader 1.4a
- Should have a custom recovery like TWRP installed
You can use this thread to install the FireFireFire bootloader and install a custom recovery. Once done all you need to do is download the Android 4.3 rom and gapps from here, place the zip files in your Kindle Fire’s internal memory and flash them in recovery (rom followed by gapps). Make sure to do a factory reset from recovery before flashing the zip files and also take a backup.
In case you need to root Android 4.3 instructions are available here.