User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:69.0) Gecko/20100101 Firefox/69.0

Steps to reproduce:

On my PC FF browser the bookmarks are synced with the central FF store. However, when one of the devices is not active for a longer period, month or more, and then activated the bookmarks sync behaves not as desired.

Actual results:

It doesn't just update all the bookmarks on the old device, but rather merges them with the newest ones in the store. As result lots of new and actual bookmarks are being lost and lots of old and supposedly unnecessary bookmarks are being restored. That is not desired.

Expected results:

The best solution would be as in the former xmarks plugin - an additional option to be introduced in the bookmarks sync configuration page, consisting of 3 buttons, allowing the user to choose whether to merge the bookmarks of the current device with the central ones, whether to ignore the local bookmarks and completely download the ones from the server or whether to ignore the ones on the server and upload completely the ones on the current device.
Besides keeping the most recent bookmarks of the user such a solution would significantly speed-up the data exchange when option 2 or 3 are chosen. That would be especially useful for the case when a new device is introduced.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

The priority flag is not set for this bug.
:markh, could you have a look please?

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Thanks for the report and sorry for the delay. We're very sorry you had this issue, but thanks for reporting it and we take these reports seriously.

For better or worse, Sync doesn't support the kind of UI you recommend - it did in the past, but we found it extremely difficult to word it in such a way that most users understood what was being asked - sadly we found that many found it confusing and chose the wrong option.

Without further details it's going to be impossible to know exactly what happened in your case - we've a few bugs on file for this so I'll close it as a dupe of one of them. The good news is that we are working on a new bookmarks engine which hopes to resolve many of these issues in bug 1433177.

Again, sorry for you having the issue and thanks for reporting it.