Hiya,
I have updated this to work with firmware 5.1.0.
I removed some of the previous functionality which has now become obsolete, so the bare-bones installation only offers usbnetwork toggle. I verified this to still be working. Other extensions should continue to work, but I'm not giving any guarantees.
I'm calling this version 1.1.0, and it's available
here. Note that this version is
ONLY for firmware 5.1.0 (or possibly newer). This version
doesn't work on older firmwares, just like older launcher versions don't work on newer firmwares.
PS: It seems like with firmware 5.1.0, Amazon has unfortunately returned to their practice of aggressively obfuscating java code. This makes it a pain in the ass to understand what is going on -- but of course it doesn't prevent it. I don't understand this short-sighted decision. I personally think that we have come up with quite a few enhancements which make the Kindle more useful and interesting to users. Now it seems like Amazon is again determined to stifle evolution. Ah, whatever, I guess some people never learn.
PPS: If someone at Amazon reads this: I mean it. People enjoy open systems, developers and users alike. By trying to lock people in, you're only locking yourself out from opportunities.