Been trying to isolate what setting might do this. My first thought was dom.storage.enabled. Nope, that’s set to the default of true.
If found this post:
http://superuser.com/questions/629525/how-to-control-websites-use-of-localstorage-in-firefox
Which says:
“disabling cookies disables storage, unless the site is on the whitelist
…
if the cookie preferences are set to prompt, this is treated the same as reject cookies”
I have my Firefox cookie preferences set to “Accept cookies from 3rd party sites, keep until ‘ask me every time'”. I changed that to until ‘I close firefox’. and it starts working.
So… Preferences -> Privacy -> Exceptions… -> In the “Address of website:” box, add my OSPi address and click “Allow” to always accept cookies from OSPi, which apparently also allows offline storage. Type in my OSPi URL and – It works!