Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Note that your System Details List shows multiple Flash plugins. Shockwave Flash 15.0 r0 Shockwave Flash 11.8 r800 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\

Your System Details shows;

Installed Plug-ins

Shockwave Flash 15.0 r0 Shockwave Flash 11.8 r800

Having more than one version of a program may cause issues.

Flash is notorious for not cleaning out the older version as part of an update. Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac Then reinstall the latest version.

Shockwave Flash v15.0.0.152 http://get.adobe.com/shockwave/

Thanks!!