How do I prevent FF Sync from updating current bookmarks on main device with the synced ones previously?
I used FF sync about 2 months ago on my main device (logged in) and when I logged in on my main device and synced, my bookmarks from 2 months ago overwrote my current bookmarks. How do I prevent this from occurring? I know to recover from this you can restore the bookmarks from previous dates using the restore & backup option off the Bookmarks menu item.
The only reason I can figure out why this occurred was that when I looked at my devices connected, my main PC was listed twice. Once as the current device subtitled, the other just listed as my PC name on my network and the other device was my laptop. So I figured I'd remove the 2nd occurrence of my main device and the bookmark problem did not occur again after logout and login, sync. I would recommend either fix the occurrence or "bug" of the main device being listed twice or add a popup or dialog box after pressing sync or selecting sync to overwrite synced bookmarks with current bookmarks on main device.
Sync is intended to synchronize Firefox data across multiple devices. It should never "overwrite" any data, but always append or merge data from other devices.
That said, "I used FF sync about 2 months ago" and the lack of mention of a 2nd device leads me to think that you were using Sync as a "backup medium"; not the intended purpose of the service.
And, Sync should never pickup the same device and the exact same Firefox Profile as a "2nd occurrence" of the same device / Profile. If Sync was disconnected for that whole 2 months, that could have played a part in your issue. Sync is made to run unattended and to constantly "tweak" any differences in data each time Firefox is launched.
One last thing, the Backup feature and Restore option shouldn't be mentioned "in the same breath" as Sync, the Backup JSON and JSONLZ4 files don't merge bookmarks - those files will overwrite any existing data. Export & Import in HTML format will append any existing bookmarks; but the Export needs to be done manually - the bookmarks.html file (if you have one in the Profile folder) isn't automatically updated daily as it was years ago. IOW, Sync is basically the opposite of Backup / Restore so far as appending vs. replacing in total.
As far as "fixing" Sync for the issue you mention; sounds like user misunderstanding of how Sync works or user error by removing that device rather than editing the Device Name via Change Device Name (if that was a new Profile that was created or a Refreshed Profile since Sync was disconnected).