Can you post a link?

Do you have disabled plugins?

A possibility is to check the page source or use the inspector to see if you can identify the MIME type or file extension.

Great suggestions for the first steps. The website is: http://www.aa.com/newamerican Based on what I experienced, the problem is in their "videos" section. It looks like they're using flowplayer to do this. (They may also have a problem defining the div for video2.) When I go to flowplayer.org, their first video will play once before generating the "plugin disabled" error. So it looks like this is where things are coming from, but I can find no flowplayer plugin; the only related item is Shockwave Flash, which is up to date, and runs other things fine. Suggestions?

I see an HTML5 video player that plays WebM movies on that page.
That player has a flowplayer link displayed on it, but that doesn't mean that the Flowplayer is used.

The Flowplayer doesn't work for me though because if I disable WebM then I see a blank empty area.

I don't seem to have anything defined for WebM. I also force-updated Firefox, and on the restart, the splash page also had a WebM that just showed the plugin disabled message. (attached) Suggestions? Do I need to add .WebM to my associations, and what should it link to?

I had this problem today viewing a video on the JW Player website. I managed to narrow the problem down to this one plugin: RealNetworks(tm) RealDownloader HTML5VideoShim Plug-In (32-bit) 1.3.1.2

Of course other RealDownloader objects may be involved as well.