Previously, the dimension of ICO format images (favicons) with multiple resources was based on the smallest resource, which is usually 16×16px. Starting with Firefox 43, the largest resource will be used instead as the intrinsic image size.
While this change should not negatively affect the browser’s UI including tabs and bookmarks, ICO images embedded on a Web page, using
<img> elements, CSS
background-image or other properties, might be displayed in different sizes unless the the
height are set.