Hello, Tab Stash has had the ability to sync via Firefox Sync since day one. Tab Stash saves your stashes as Firefox bookmarks, so there's no need for a separate sync feature—all you have to do is turn on Firefox Sync on each of your devices and you should see your stashes everywhere.

You can always find your stashed tabs in "Other Bookmarks" > "Tab Stash". Even on Android, on iOS (where extensions aren't allowed at all), or if you uninstall Tab Stash entirely, your stashes will be there for you to use.

Hope this helps!