Created attachment 799919 [details] 名称未設定.jpg User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:23.0) Gecko/20100101 Firefox/23.0 (Beta/Release) Build ID: 20130814063812 Steps to reproduce: First, install Firefox23 into MacbookPro with Retina model (middle 2012), and newest FLASH player (in MacOS X 10.8.4). Next, one play FLASH movie (like as Youtube, Oficcial Site of some movies, and so on). Actual results: In FLASH player, movie work on only upper left 1/4 area (look attached file). Other areas are becoming blank space. When I roll back Firefox version into ver.22, this problem is not working.