[saelwell]

Yup. That all seems to have worked now. I didn't want to try the JB without advice in case I broke something. The restart showed the *** MKK K JB *** message.

So the solution was:

Kubrick debrick to firmware 5.2.1 plus clearing out local settings
Update firmware with Amazon updates to 5.3.7.2
Jailbreak 1.14.N

Thanks knc1 - I guess you hit the nail on the head in suggesting the Kindle had something dubious installed on it.

Thanks to both knc1 and NiLuJe for your patience in seeing me through this. A big learning curve but I am the better for it. I appreciate your expertise and am glad in a funny sort of way that it wasn't a trivial problem, which means I don't feel too much of a numpty and that the few hours of my time (not to mention yours) were actually spent constructively.

Cheers, Stephen