Use with Extreme Caution;

Bookmark Duplicate Cleaner {web link} Scans for bookmark duplicates and allows you to delete them

Bookmarks Checker - check for bad links {web link} Check favorites for broken or bad links. It checks for bad links and displays a report if it finds something. Check for 404 links, timeout links.

Any chance that one of your devices runs a "mobile" Firefox; like Firefox for Android or Firefox for iOS? "Mobile" seems to be 'introducing' corruption into the Sync process; or the Sync server is screwing up desktop / laptop when a "Mobile" device is connected to the Sync account, for possibly as long a 6 months now based support threads here since (maybe) June or July 2015.

"Merge" is what Sync does. There's no user control like to select a master device, with the others being a "slave". All desktop / laptop installations are equal, and should have the same bookmarks via merge. The "mobile" devices will be slightly different, especially the "Bookmarks Toolbar folder being unique to the "mobile" devices. Desktop / Laptop device will have a folder named like "Mobile Bookmarks" or "Mobile Toolbar Bookmarks".

Depending upon how many PC's are involved, how many bookmarks are involved, and how long each PC has had Firefox open for an after the initial Sync process, it might tale awhile for the entire synchronization process to be completed.

Overall, my advice isn't to try to fix the duplicates but rather to run Places Maintenance to fix the Places database on each device, after disconnecting from Sync. Once the 'maintenance' is completed reset the Sync password to clear the corrupted data from the server and reconnect the first device to the Sync service and let Firefox run on that device for at least an hour. Then connect each other device in similar fashion; don't be in a rush to get all those devices connected back to the Sync server.

Thank you all for you answers.

@--> the-edmeister

You are right.I wrote only pc's but are some android mobiles too which i synced with mobile firefox.

So i will try your suggestion but since there is an ongoing problem with firefox mobile should or should not sync again mobile devices?

Regards, the_observer.

As I suspected, "Mobile" is involved. I don't recall even one support thread where this "duplication" was occurring with Desktop / Laptop devices alone and 'they' are the installation that are affected - not the "Mobile" devices.

At this time I wouldn't include a mobile device in Sync, at least as far as Bookmarks are concerned.

I have been attempting to track reported issues with "Mobile" possibly corrupting Sync bookmarks on "Desktop", but too many threads aren't closed by the "Owner" with a solid answer as to whether the problem has been solved and/or exactly what their solution was or was left unresolved or inconclusive.

And I haven't even found a Bug report filed about this issue. Then again my search fu skills at Bugzilla have always been poor at finding the Bugs that I am looking for.

And since I don't even have a "Mobile" device I'll never see the issue I "see" in these support threads for myself. All I can say is that over the past three months I have seen enough of these "bookmark duplication" threads where "Mobile" is connected to think "Mountain View we have a problem!" - like with NASA = "Houston we have a problem."

Overall, I figure that an enhancement was made to Sync right about the time that the Beta version of Firefox for iOS was made public last summer, and soon after that "we" started getting these 'duplication' reports here. I believe the enhancement was to provide Sync and the browsers with separate Bookmarks Toolbar folder for "Mobile" and "Desktop": Mobile bookmarks toolbar is a lot shorter that the Desktop bookmarks toolbar area - so Mozilla provided for two different types of displays, as near as I can deduce.

Please post back as to what you do and provide results if that corruption reoccurs with "Mobile" out of the mix.