2. Notes source code is at https://github.com/mozilla/notes, the panel.js source...

2. Notes source code is at https://github.com/mozilla/notes, the panel.js source[1] is the one that saves and load content. It uses the Storage API from Web Extensions[2], but it uses it only to save/load locally. It is not currently sending any data anywhere. So, sync is not enabled. If you click the sync button, you're greeted with a message[3] saying it is not implemented yet (they do count it and metrify it, probably gauging interest).