Localhost development throwing security_manager_veto errors during certain interactions with the beforeunload event.
The default "leave the page" warning shows up and pressing cancel and then refresh or just refresh while the dialog was open kept throwing the error.
Mozilla's suggestion for preventing the popup
window.addEventListener("beforeunload", function (e) {
var confirmationMessage = false;
e.returnValue = confirmationMessage; // Gecko, Trident, Chrome 34+
return confirmationMessage; // Gecko, WebKit, Chrome <34
});
Was ineffective.
EDIT
Problem was due to jquery handling beforeunload events in the background.
Using the answers on another SO question here and unbinding the onbeforeunload using jquery, the problem was fixed.