It's not, strictly, a glitch; it's a bug in the security of the update system.

Firefox turned it off because otherwise the update system could be used to completely own -- totally circumventing all of the core update security mechanisms -- your firefox install. (Firefox is effectively an operating system. This is the bad side of that.) This has been an increasing problem with all browsers; malevolent actors push a browser version they own via the update, and from the user perspective neither you nor your anti-virus can tell. It's a browser application with automatic updates and security certificates and everything, just malicious ones.