I thought I'd be the first one to report it but alas, wasn't entirely sure yesterday. Anyway, +1 to successful jailbreaks on 5.8.10 (KT3, G000K9). And yes, I'm sure cause when I got the kindle a month ago, I was super disappointed to learn that it meant no more covers screen saver for me.
On a whim I decided to try it anyway. I actually did both, setup wifi and register the device after factory reset, before going into the airplane mode. Got the downgrade thing from here:
http://www.mediafire.com/file/w7zz4o....0_initial.bin (apologies, I'm not that computer savvy to know how to check the sums). For a while it appeared stuck on that kid-under-the-tree picture (yep, I did panic some ^^) but from there it went on without a hitch.
So... big thank you for getting me my covers back!