Board Thread:Support Requests - Designing Your Wikia/@comment-14443911-20160131105128/@comment-4530178-20160131105818

It's called a favicon. To change the favicon, on your wiki, go to Theme Designer → Wordmark → Favicon. In the favicon section you can upload a .ico file (has to be 16 x 16 pixels) and Wikia will do the rest for you!