Mozilla Firefox will use Windows Background Intelligent Transfer Service, or BITS, to download software updates in the background. This is the first step in the eventual release of a standalone “Update Agent”” that will perform updates even when the browser is closed. This should make updating more convenient for everyone and reduce the time to get new updates for users who aren’t well supported by the current update process because they don’t run Firefox very much and/or they have slow Internet connections. Mozilla is using BITS because it allows updates to be downloaded in a way that can be recovered in the event that a download is halted for some reason.”
Source: https://www.bleepingcomputer.com/news/software/firefox-to-use-windows-bits-service-for-background-updates/