What video and what site?

pretty much anything except You Tube. Primarily news related sites:

cnn.com channel3000.com cnbc.com

Most sports sites like espn.com work fine.

Is Flash the problem or is it something else I'm doing right? I worked fine before Mozilla started messing around with Firefox.

See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

Make sure you are not blocking content.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

When you're on a page that wants to use the Flash plugin, do you get the plugin notification icon displayed toward the left end of the address bar? It looks like a gray "Lego" block. That icon is to manage the site's permission to use Flash.

If the icon does not appear, and you've ruled out add-ons, two other thoughts:

(A) Do you use any video recorders/downloaders/catchers that may insert themselves between Firefox and the site?

(B) Has Firefox raised any objections to secure site certificates (untrusted connection) recently?

Regarding safe mode - The videos play fine in safe mode, so it may be something with my add-ins (Adblock, Adblock Plus, NoSquint and Print Edit WE)

Regarding plugin notification icon - when I disable my AdBlock add-ins video runs fine, but the Flash icon doesn't appear, which means that these sites must use something else to play video (which my adblocking add-ins are keeping from running). I guess this means if I want to watch a video I have to disable my adblocking add-ins.

Problem solved - I allowed the websites to run without the ad blocking add-ins. I had to exclude those sites.

Thanks to everyone for their help solving this problem

Well done.