I think we might run into a mixed-content warning in IE7 when loading data-encoded images when using HTTPS ([more info](http://robm.fastmail.fm/articles/ie7-dataurl.html)).

There are other data-URL encoded images in tabzilla, but only in an ```:after``` pseudo-element, which IE7 conveniently ignores. Maybe instead of the empty italic tag, we could use :after here too?