I’m currently using local storage in both of my extensions.
When converting my first extension to webext, I tried using sync, but it kept crashing, so I stopped using it.
If, at some point I chose to use sync, I would have to keep storing some things in local (for example the list of domains to clean on startup).
Obviously, there is an issue with storing the list when multiple devices add or remove entries.
I guess I would keep the current list in local storage and then create a map of lists in sync storage.
This map of lists in sync would need some unique ID for the device as the key.
Each device would then store the action (like create, update, delete) together with a timestamp in this device specific list, so when a sync update has been received, these changes can be easily merged as needed, maybe with user permission.
Not sure if there is such a device specific unique ID tho… I haven’t had the time to research it.