In case this helps anyone I rolled my Firefox back to version 56 and FVD Speed Dial to version 62.8.5 and my speed dials were back. I took the opportunity to save them to a file. I then updated FVD to latest version and then updated Firefox to latest version, this time the dials didn't disappear. Previously Firefox was updated and FVD was updated automatically.
In case this helps anyone I rolled my Firefox back to version 56 and FVD Speed Dial to version 62.8.5 and my speed dials were back. I took the opportunity to save them to a file. I then updated FVD to latest version and then updated Firefox to latest version, this time the dials didn't disappear. Previously Firefox was updated and FVD was updated automatically.
Hope this helps some one.