Board Thread:Support Requests - Getting Technical/@comment-26474238-20130928222720/@comment-1158325-20130928231935

What you linked to isn't an extension, it's just part of HTML. What you see on WoWHead is most likely done with JavaScript, though I don't know where to find the code for it on that site. One of these extensions may do what you want, but I'm not familiar with any of them. If you know of any Wikia wikis that do something like that, you could ask them what they use.