The chat ads that are shown in the side bar of site pages incorrectly expect the user to always have a gravatar-based profile image:
var e = "http://www.gravatar.com/avatar/" + b.emailhash + "?s=23&d=identicon&r=PG"
This is incorrect behaviour for users who have Facebook or direct-upload profile images. As Szabolcs points out in chat, this is a particular problem for Facebook images which have their own query string, as it breaks the size argument to gravatar:
emailhash value is a URL, and use that in place of the constructed gravatar URL when appropriate.
For the related issue of the icon being allowed to be too large, the generated
<img> tag should be constrained to
height="23" width="23" just in case.