You may need to downgrade to Flash 11.2 or 10.3. There are known issues that Flash & Firefox developers are working on. Unfortunatly we keep modifying advice as the situation changes.

Current advice _{Recent crashes of certain multimedia contents (this includes Youtube videos, certain flash games and other applications) in conjunction with Firefox 13 are most probably caused by a recent Flash 11.3 update and/or a malfunctioning Real Player browser plugin.
In order to remedy the problem, please perform the steps mentioned in these Knowledge Base articles:
Flash Plugin - Keep it up to date and troubleshoot problems
Adobe Flash plugin has crashed - Prevent it from happening again
Flash 11.3 doesn't load video in Firefox
Other, more technical information about these issues can be found under these Links:
http://forums.adobe.com/thread/1018071?tstart=0
http://blogs.adobe.com/asset/2012/06/inside-flash-player-protected-mode-for-firefox.html
Please tell us if this helped!}

You may need to keep checking links such as the next one, for revised information

• Adobe Flash plugin has crashed - Prevent it from happening again we are trying to keep the article updated,-and it links to other Flash 11.3 & FlashPlayer troubleshooting information
• A related, but long & techi up-to-date article is http://kb.mozillazine.org/Flash#Flash_Player_11.3_Protected_Mode_-_Windows

A separate issue involves the use of RealPlayer if you have Flash Player problems, please at present always mention wheter you have any Real Player software installed.

Your "more system details" shows the "RealPlayer Browser Record Plugin" extension is installed. Even though it is disabled, it is causing the errors at YouTube and other Flash problems, which are caused by the new "Protected Mode" feature in the Flash 11.3 plugin.

You need to open RealPlayer, go to "Preferences -> Download & Recording" and uncheck "Enable Web Download & Recording for these installed browsers", then click OK, close RealPlayer and restart Firefox. This is the solution currently given in the Flash 11.3 doesn't load video in Firefox article.

For more information and other possible workarounds, see:

• http://kb.mozillazine.org/Flash#Flash_Player_11.3_Protected_Mode_-_Windows

I looked into the settings for RealPlayer and found it was set up to only work in either MSIE or Google. I unchecked that box and I'm no longer experiencing any problems. Thanks to all who commented!

Thanks for posting back. Glad the issue is fixed.

BTW I believe RealPlayer may have released an upgrade release within the last day or so. It is possible part of the reason for that is to fix the problems with Flash 11.3 (Windows Vista and up) & Firefox 13 compatibilities.

I uninstalled Real Player and the problem away. I was then able to see youtube videos with Firefox.

The issues with RealPlayer and Flash have been fixed in RealPlayer 15.0.6 so another alternative is to update RealPlayer to the latest version. Ref:

• http://kb.mozillazine.org/RealPlayer#RealPlayer_Browser_Record_Plugin_extension
• Flash 11.3 doesn't load video in Firefox

I downloaded Real Player 15.0.6 and it worked with Firefox and streaming youtube video. Looks like Real Player fixed the problem