Changes

|Feature overview=Synchronize addons Add-ons are synchronized between installationssync clients.|Feature users and use cases=TODOUser installs an add-on on one browser. When a sync occurs, the add-on is automagically installed on other sync clients.|Feature dependenciesfunctional spec=* Wait Add-ons are only synchronized between similar client types (e.g. desktop and mobile). In other words, the add-on set for async engine support?|Feature requirements=|Feature nondesktop clients is independent of of that of mobile. The reason for this is add-on compatibility. At the time this was written, most add-goals=|Feature ux design=|Feature privacy review=|Feature implementation notes=ons did not function properly on desktop.