Mozilla Firefox users are reporting that when they upgrade to the latest Firefox 67, they are finding that their addons are missing, their customizations are gone, and their history is gone. Mozilla has switched to an individual profile for each installed version of Firefox. This means that a Firefox Nightly install would use a different profile than an installed Beta or Stable build. Mozilla developer advocate Dan Callahan, stated that this behavior is most likely being caused by the new separate profile-per-install change in Firefox 67.
Source: https://www.bleepingcomputer.com/news/software/firefox-67-switching-to-empty-profiles-causing-data-loss-fears/