If you don't want this you can change things.

When you first install Firefox, uncheck install updates as a service. Personally, I don't like applications running services in the background all the time. When I close something I expect it to be gone, and I don't want it running until I tell it to.

Second, go into settings and change your update settings to "Check for updates but let you choose to install them". Firefox will pop up with a discrete notification telling you when an update is available, asking you to download, then another dismissable notification telling you to restart to update.