The latest update for Adobe Flash, version 11.3 does not play well all the time with Firefox.
The symptoms are that you go to a page with a video and it won't play, it will show as a black or grey box, or simply fail to load. If you want to see Firefox's help page on it, you can read all the details there.
The suggestion is to "downgrade" Flash to the older version.
Luckily here I am not seeing the problem since I tend to be slow on Flash upgrades unless I see warnings on websites of dire doom and gloom. They seem to be upgrading Flash almost every time I reboot this computer.
Personally, I think it's a great technology that's time has passed. There are other ways to manage that sort of video such as HTML5, which is coming down the pike.
If you are having some problems seeing the video that I have embedded below, you may want to follow this help link at Firefox's website for more hints.
The video is one of Border Collies herding sheep and is safe for all audiences.
Who doesn't love Border Collies? Awwww! CUUUUTE!