Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 15.0 r0 Shockwave Flash 11.2 r202

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/

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences<Enter> in the address bar

Select Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.