Some types of videos require some plugins to work, because Firefox doesn't have native support to this MIME type then you need a plugin to have access to the content.

But be careful some websites show fake messages, trying confuse the user, giving fake links, usually giving links to malwares or malicious pages.

Your system details list doesn't show that the Shockwave Flash plugin is installed and enabled.

• Firefox/Tools > Add-ons > Plugins

You can find links of the latest Shockwave Flash player for Firefox on this page:

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