Restore a specific sync from Firefox Sync
I was transferring my data from an older version of Firefox to the new version and always have enabled Firefox sync.
While setting up the new browser, I uninstalled an extension that had my settings from the new browser and it was automatically uninstalled from the older browser too.
Since I use Firefox sync, I want to know if it's possible to restore a restore the extension data from a specific time (before I deleted it). Trying to sync only restores it after the extension was deleted.
That data is no longer available once Sync has done its things. Note that you should always disconnect Sync if you make changes to items that are synced to other connected devices.
See also "Can I have different enabled states on different machines?"