I kept losing my container data due to Firefox sync errors. Every week I reset Firefox on one of my 4 devices because it stops syncing new container data. By using this extension, I made a backup from my main device and then did a restore on the affected devices and to my surprise, it worked perfectly. It even synced website data + the names of the containers.

Works perfectly. It need sometime to update.

Last version at 6/3/2018 works fine (Synced from Firefox release to Firefox Beta ). You should have already installed the containers plugin (which for some reason firefox is not syncing, but that's different story), then this add-on will work