changed password without user confirmation, lost data. backup bookmarks or they will be lost. doesnt actually work after a while. 5star reviewers lie or gave 5 stars too early.

turn off the sync to use it

After a Firefox update, my password doesn't work anymore. It seems this happened to other people too. The addon hasn't been updated in two years so I don't recommend using it. If you do use it you should regulary export your private bookmarks as plain text file

this extention won't let me add any bookmarks

RSN

All in all: good idea but problematic expirience.
It deleted my hidden bookmarks - probably in a sync between two machines running at a same time, but there is an option to RESTORE bookmarks so it is not the end of the world. Can't wait to see it fixed.

It seems the function to "sync bookmarks and preferences across devices" is broken as of at least Firefox 84. While it was enabled, I was unable to make any changes to the bookmarks I had (anything I added, deleted, renamed, ...) was reverted everytime I closed Firefox. With that feature off, it seems to be working fine. A little less useful than before, but better than not working any more at all. :-)