Failed on KT3 (8th gen) running Kindle 5.12.2 (356965 025).
The experimental browser gave some error about how it can't open that kind of file.
Trying to save my ooold Kindle I haven't used in years from the awful GUI update. 
Wait, nevermind. Missed ones of the 3 slashes!
So what do I do now to keep it from ever updating? I am confused.
PS It still keeps downloading update.bin.tmp.partial into the device.
I'm just repeatedly deleting it.