The primary fix in v66.0.5 addressed a remaining issue where web extensions were still disabled for users with a master password set.
Prevents web pages from "jumping" while images and advertisements load. Mozilla Firefox Quantum v66.0.5
A new ability to search through all open tabs via the tab overflow menu. The primary fix in v66
Allows users to authenticate on websites using facial recognition or fingerprints on Windows 10. System Requirements Firefox 66.0.5 System Requirements Mozilla Firefox Quantum v66.0.5
Automatically prevents websites from playing sound-enabled media.