Are the firefox settings under category Sync, ok, open tabs ?

sadolino said

Are the firefox settings under category Sync, ok, open tabs ?

yes this is checked. I have some tabs open on machine A where 5 of them are pinned. on machine B I see all the tabs in the sidebar but the pinned tabs of machine A are not in there nor are they pinned out of the box (what I would have found a nice feature that all my machines have the same pinned tabs and pinned tabs are in sync over all machines). I am asking because I don't know if it should work but doesn't or if its just not yet implemented.

On machine A, they aren't pinned and in the bookmark section or they only don't pinned but are in the bookmark section ?

Try to reinstall firefox on machine A.