Website favicons in the Firefox viewport

A website favicon loaded into the Firefox viewport by entering its URL in the address bar will also be displayed in the tab and the address. In this case, Firefox does not load the tab and address icon from the web domain’s root folder — these icon images are loaded from the browser viewport.

Firefox does this for all images rendered in its viewport as stand-alone images rather than as image elements within a rendered page. To see this behavior, right click any image in a rendered page and select View Image.