The HTML Browser API is an extension of the HTML <iframe> element that allows web apps to implement browsers or browser-like applications. It currently works in (privileged) chrome code on Firefox desktop (version 47 and above) and privileged and certified apps on B2G/Firefox OS.
The DataStore interface of the Data Store API represents a retrieved set of data, and includes standard properties for accessing the store's name, owner, etc., methods for reading, modifying and syncing data, and the onchange event handler for reacting to changes to the data.
The DataStoreChangeEvent interface of the Data Store API represents the event related to a record changed in the data store, i.e. this is returned once a change is made and the change event is fired (see DataStore.onchange for the handler).