Since these sites tend to be video-heavy, could you test disabling the protected mode feature of the Flash player plugin. This feature has security benefits, but seems to cause unresponsive script errors on some systems. There is a hidden setting for disabling it: (A) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful. (B) In the search box above the list, type or paste '''flash''' and pause while the list is filtered (C) Double-click the '''dom.ipc.plugins.flash.disable-protected-mode''' preference to switch its value from false to true. This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox.