Re: In a .net CMS environment (Hubspot) using Fancybox 1.3.1, jQuery 1.4.2 and a Youtube iframe - FF in Windows 7 will not play videos. FF mac does. What gives?
There are some compatibility issues between the latest Flash player and some Firefox add-ons or settings. Could you see whether anything in this article helps: Flash 11.3 doesn't load video in Firefox.