In Windows 8, sites that use Flash use the built-in Flash player provided in Internet Explorer 10. Microsoft maintains a Compatibility View (CV) list that has sites that are blocked (this is a recent change as of March 2013. Before that, the CV list maintained sites that were allowed).
However, for developers testing their sites on Windows 8 using Internet Explorer 10 can make a small addition to their registry to see that site light up. For instance, when I was making my new MOO card, I was using my Surface RT device and the site’s card designer uses Flash. I made this small change/addition to my registry and boom. I was designing my card without a problem (the screenshot above is from my Surface).
Here is what you have to add/change:
Add the site (without any http or / slashes). This will cover not only the main domain, but any subdomain hanging off the main site. For instance, I simply added “moo.com” (without the quotes) and even though the site redirects me to http://us.moo.com, the Flash worked fine.
Note you can add only one site at a time and it is not recommended to mess around with your registry unless you are completely comfortable doing it.
For more information and details on the Compatibility View list and adding Flash sites, see this MSDN article.