After installing a Firefox update sometime around July 2013, I was no longer able to play DVDs in either Windows Media Center or Windows Media Player. I can still watch Youtube videos, etc. After a lot of internet research I saw that other people had this problem after installing a certain plug-in with this Mozilla update - and the only way it was resolved was to stop using Mozilla or uninstall Windows Media Center and Windows Media Player. I do not want to uninstall either of these, but I love Mozilla, so I'd like to fix this. From what I have read, the only way to fix this is to do a factory reset on the computer to get rid of the plug-in. I tried uninstalling and re-installing Mozilla, and that did not solve the problem.