The Windows version of Firefox can now automatically upgrade itself to the latest version in the background when the web browser is not running. The feature was first rolled out to Windows Nightly users on April 12 in the form of a Background Update Agent. Mozilla first announced that the feature was under development more than four years ago as a background process designed to check for updates and apply them for users with slow Internet connections and/or who don’t run Firefox daily. There are no immediate plans to implement the feature for Windows or Linux users.
Source: https://www.bleepingcomputer.com/news/software/firefox-now-autoupdates-on-windows-even-when-not-running/