We changed IndexedDB in FF16 to not require a prompt. Unfortunately, that seems to mean that callbacks that would usually fire when the prompt is clicked aren't being called on mobile. http://people.mozilla.com/~mbrubeck/test/idb.html
I think this is a bug in the test page. Modified version works fine on a private local build: http://dl.dropbox.com/u/72157/idb.html Closing invalid. Reopen if I'm wrong.
Yes, you're right: mbrubeck's test had a bug. But the bug was with the warningQuota prompt, not the initial "allow to use IndexedDB" prompt. Opened bug 805560 (so this one can stay closed).