This is some standard guidance that addresses the most common reasons for Flash problems in Firefox. I'm sure you've seen some of it before, but just in case:

(1) If you have any recorders/downloaders that interact with Flash media, make sure they are as up-to-date as possible, or disable them temporarily.

(2) Disable hardware graphics acceleration in Firefox and in Flash

(A) In Firefox, un-check the box here and restart:

orange Firefox button (or Tools menu) > Options > Advanced > General > "Use hardware acceleration when available"

(B) In Flash, see this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

(3) Disable protected mode (Windows Vista and higher)

See this support article from Adobe under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

Hello,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

Go to Firefox > Help > Troubleshooting Information. Click the "Reset Firefox" button. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish. Firefox will open with all factory defaults applied. Further information can be found in the Reset Firefox – easily fix most problems article.

Did this fix your problems? Please report back to us!

Thank you.