@ AndrewGSW: seems to work OK, your idea, provided you're grabbing the textContent of the iframe in Chrome and FF. IE wants to download the json file
@ rnd me: I'm not producing the json - that's the problem. I wasn't aware that ajax worked offline, too. thanks for the tip. I'm really quite clueless about the whole offline thing in general. I've looked over the links you posted in this thread
and they were very useful. I guess I'll google around for using ajax with manifests, unless you have something handy...?