can't login to everhelper: an error occurred. please go back to the login form

Have not seen a solution for this.  Want to sync/merge my dials. When trying to login to Everhelper,- an acct I created just for this - the login fails with: "An error occurred. please go back to the login form".  If I instead choose to login with my Gmail acct, it works, but all sync processes fail.

Firefox version is 62.0 62-bit

This problem started a few months ago with previous version of FF.  Removed FVD Speed Dial, reinstalled, and restored dials from file.  Problem persists in sync/merge actions, which basically renders this add-on useless, which is a shame.