Bug 41730 – Injected scripts cannot observe beforeload events from elements that start loading before they are inserted into the DOM.

• Component: Page Loading
• Status: NEW

[Andy Estes]

Injected scripts need a way to observe beforeload events for elements created outside of the DOM then inserted on load.  For instance, the beforeload event for the following image will not be observable by an injected script:

var img = new Image();
img.src = ...;
img.onload = function() {
   parent.appendChild(img); 
};

One solution is to have beforeload events from fragments propagate to the document element.  This would allow document-level beforeload listeners to respond to beforeload events from fragments, but would cause beforeload event propagation to diverge from other DOM events.