When trying to fix a problem, I uninstalled Flash Player and attempted to reinstall it. It downloads ok, but after asking to "run", it does not complete. Nothing happens. I am running Firefox 25, Windows 7 32 bit. On of the problems I had was that when viewing a video, it would freeze unless the mouse was moved. This also began to happen in Firefox.
Download the Adobe Flash Player installer directly by right clicking one (or both) of the following links and selecting the "Save as" option.
Reboot, and then run the installer(s) from your downloads folder.
See: http://forums.adobe.com/thread/891337 to disable hardware acceleration, as that usually leads to freezes when streaming content.