I use the most recent version of the above mentioned browsers. I started with Opera and IE Sync which was already a big mess and I had to clean up tons of duplicates (>6.000 instead of 1.200 bookmarks). Now I needed Firefox and tried the extension there too to get my bookmarks. It downloaded my bookmars as expected but the sync does not work.
1) Sometimes duplicate empty folders are created
2) Deletion of bookmarks is not synced (any direction)
Customer support service by UserEcho