The images for the thumbs do not work for me in Safari. The reason is the following:
TypeError: 'undefined' is not an object (evaluating '$box.removeClass( 'mwe-popups-no-image-tri' ).find( 'image' ).setAttribute')
The reason is that no <image> was added but a <img> instead. This is because some browsers (IE and safari) basically have a symbolic link from image to img in the HTML context.
And that leads us to the 2nd problem, these elements are created using jQuery, but jQuery doesn't support element namespaces explicitly and because the image element will be created in the 'current' document context, it will thus create an HTML img element. What you need instead is something like: