Having problems since upgrade to Firefox ver.55.

Ever since I upgraded to FF55 (or may be a couple of versions earlier) auto sync does not work. When a manaul sync is attempted, it just keeps on showing the sync dialog window.

When nothing happens for many many minutes, I cancel the dialog window. After that the manual sync button is automatically disabled. Also, the ACCOUNTS tab is Settings of the add-on shows an overlay of a sync icon which leaves account settings inaccessible.