This is a system add-on that will provide extended support for proxy failovers, ensuring that Firefox can continue to update in all network situations and regardless of which add-ons are installed. This system add-on does not have any user facing consequences, manually setting a proxy will continue to work as expected. The main case covered here is when a proxy set by an extension becomes unresponsive.We intend to make this feature part of Firefox, but are beginning its implementation as a system add-on for a staged rollout to the versions we intend to cover.