Missing favicon fallback load #1285
Description
I'm seeing the following in the Browser Toolbox:
Security Error: Content at moz-extension://1767b9bf-7192-42e7-b0d3-a51bfc1d8ce5/popup.html may not load or link to moz-icon://goat?size=16.
We should stop using the goat icon and instead have a fallback icon that is premitted to load. (we can just copy the browser default icon directlly from mozilla central
