It seams that the oldest firmware bin that was uploaded to that "s3.amazonaws.com/
firmwaredownloads/" location on Amazon's servers is 5.8.2.1. And before that the server location used was "s3.amazonaws.com/
G7G_FirmwareUpdates_WebDownloads". And that on that older location
the oldest downloadable firmware version that had "update_kindle_paperwhite_v2" in its filename is 5.6.1. (and that firmware had bunch of "bugfix" releases so you probably should just download the last one: 5.6.1.0.6):
Code:
https:/s3.amazonaws.com/G7G_FirmwareUpdates_WebDownloads/update_kindle_paperwhite_v2_5.6.1.0.6.bin
Older than that (= 5.4.x up to 5.4.5.1)
it looks like they didn't use "update_kindle_paperwhite_v2_" in filenames but used "update_kindle_" for all Kindle models that existed at the time. So the earliest PW2 firmware would be 5.4.2 (5.4.0 was probably factory firmware for PW2 and was never uploaded to firmware servers).
Code:
So the oldest pre-5.6.1 firmware links is:
https://s3.amazonaws.com/G7G_FirmwareUpdates_WebDownloads/update_kindle_5.4.2.bin
The newest pre-5.6.1 firmware link is:
https://s3.amazonaws.com/G7G_FirmwareUpdates_WebDownloads/update_kindle_5.4.5.1.bin
So, pick your poison