The only stable 64-bit Flash experience on Windows 8 came via Google Chrome . Google got fed up with Adobe’s slow 64-bit progress. They forked Flash into "Pepper API" (PPAPI), sandboxed it, and shipped a 64-bit version inside Chrome. If you used Internet Explorer 10 (the default on Win8), you were stuck with 32-bit Flash. If you used Firefox 64-bit (which barely existed), you were out of luck. The Technical Quirk: Protected Mode Hell For the engineers in the room, here is the deep cut: Windows 8 introduced a stricter Protected Mode (Low Integrity Level) for IE10.
The Ghost in the Machine: Revisiting Adobe Flash Player 64-bit on Windows 8 adobe flash player 64 bit windows 8
Have you tried turning off Protected Mode yet? The only stable 64-bit Flash experience on Windows