This will modify the "dom.popup_allowed_events" preference to control whether events from
user actions are allowed to open pop-up windows or not. If set to `false` then pop-ups from
user actions will not be allowed and will result in a doorhanger being displayed informing
the user that a pop-up was blocked. If set to `true` then all of the default events
will be allowed to open pop-up windows.
MozReview-Commit-ID: 8UFziq23zug
