I got this to work once I made sure the URLs were exact. It won't work on subdomains unless I set up an entry for each subdomain. It would be helpful have a favicon for a site and all it's subdirectories (eg http://*.example.com) and then override those where the specific URL is given. I'd also like to set up a favicon using the URL and a string that's in the path or parameter (which may also work for subdomains) so that when i have different sites open in web.archive.org I can differentiate them. The page title string isn't effective for any of the sites I need because they all use the main site name as the page title if they have one, so it would be helpful differentiate them by a common string in part of the URL.
Overall this is a huge help in trying to quickly find the tab I want when i have a lot open.