If anyone has a possible interest in jailbreaking their Kindle, do not install this update, and turn off wifi before Amazon stealth-upgrades your device without permission. The new jail-break should be released very soon:
https://www.mobileread.com/forums/sho...d.php?t=265675
You should be able to apply this update after the jailbreak. But you cannot apply the jailbreak after you update the FW.