Disable IndexDB
Firefox mumblepointoh added official support for the IndexDB API, which is yet another storage mechanism we have to worry about: https://developer.mozilla.org/en/IndexedDB
It appears IndexDB is disabled for third parties, and also prompts the user for permissions to store data for each site, but we should still be clearing it on New Identity.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information