here is the solution https://support.mozilla.org/en-US/questions/776670

Nope no solution there. This morning Youtube videos started working fine and now they arent working again, this has been happening for days now

Ok, let's try a couple of things here.

Run the official flash uninstaller: http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html

Then download and install Flash again from http://fpdownload.macromedia.com/pub/flashplayer/current/licensing/win/install_flash_player_11_plugin_32bit.exe. (Make sure Firefox is closed during this whole process).

If that doesn't work, let's run through a few more steps:

Start Firefox in Safe mode. Does it work there?

Also, try updating your graphics driver. https://support.mozilla.org/en-US/kb/how-do-i-upgrade-my-graphics-drivers. Both Firefox and Flash use Hardware acceleration, which utilizes your Graphics card to make browsing faster. Having an out of date Driver can cause problems.

Also, install all Windows Updates.

Let me know if any of this helps.

None of that has helped either

A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked