Try to disable the hardware acceleration in the Flash Player.

See:

• https://support.mozilla.com/kb/Cannot+view+full+screen+Flash+videos
• http://www.youtube.com/swf_test.html (right-click the player: Settings)

Flash "Display settings" window:

• http://www.macromedia.com/support/documentation/en/flashplayer/help/help01.html

Thanks for reply. But I think you misunderstood my situation. What i'm saying is that all embedding flash content is broken. (But i can watch streaming flash video normally in youtube.com) for example videos in Facebook or any website with those embedded content cannot display normally, but the audio is fine.

Few hours after i posted this question, i found the solution.

My solution: i removed all Adobe Flash plug-in (both 64bit and 32bit ,Active-X and Plug-in one) and re-download the 32bit version & re-install. Everything returns to normal :)

p.s. [under IE9, for 64bit & 32bit version, no problem. ]

Use this link: http://aihdownload.adobe.com/bin/install_flashplayer11x32_mssd_aih.exe

your solution don 't work for me. Firefox 7.01 have a serious problem with flash player

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")