- Add the schema itself with definitions for the various data structures the serialized browser session state contains - Add means of validating the current state against the schema with a new SessionStore.vaidateState method - Add a smoke test to the schema by validating against sample session restore document - Fix an issue in SidebaState which was returning undefined for some property values which isn't valid JSON Differential Revision: https://phabricator.services.mozilla.com/D246163