Yahoo normally has issues with its video service, your not the only one. However have you tried starting Firefox in safe mode? https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Note that your System Details List shows multiple Flash plugins.

1. Shockwave Flash 15.0 r0
2. Shockwave Flash 17.0 r0

You can find the installation path of all plugins on the about:plugins page.

• http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins

You can check the Flash player installation folder for multiple Flash player plugins and remove older version(s) of the plugin (NPSWF32) and possibly (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\

You can find the latest Flash player versions for Firefox on this page:

• http://www.adobe.com/special/products/flashplayer/fp_distribution3.html

Uninstall flash from your computer, restart your computer and then reinstall flash. Seems that it got confused about which version you have.

After the above, If you have problems with current Shockwave Flash plugin versions then check this:

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting