In late Feb 2015, MTurk's favicon changed from the Amazon AWS-style orange box/cube to the Amazon.com-style 'a' with a smile/arrow. Since the login page uses the Amazon.com-style favicon, as do Amazon.com product pages, it's now less convenient to tell them apart from MTurk pages in your tabs. So this script brings back the distinctive AWS-style favicon for all MTurk.com pages.
See also: my MTG thread post
For many more MTurk-related userscripts, see the Turking Scripts set