Embedded video not playing in Firefox

Question

I can play video on the youtube website, but I cannot play youtube videos embedded in facebook or other websites. Captchas are also not showing up, I suspect the two problems are really the same problem. This started about a week or two ago.

Answer 1

"... I already tried uninstalling and reinstalling firefox."

Uninstalling and reinstalling is mostly a waste of time for problems with your browser. You should look at these two references:
Troubleshoot Firefox issues using Safe Mode
and
Use the Profile Manager to create and remove Firefox profiles

Problems with browsers commonly arise because of

• some extension/plug-in the user installs or removes or which is updated or which stops working after an update to Firefox.
• corruption of some aspect of the user's profile.

To elaborate, whether an add-on or plug-in is responsible for your problem, a "safe mode" is available and its usage is detailed in the first link.
A corruption of some file, a relatively rare situation, can be deduced by using a different profile as described in the second link.
Note that backing up your valuable data such as bookmarks is a must.

Answer 2

It turned out that the culprit was the Google Disconnect 2.4.2 add-on. Disabling it fixes the problem. I am using Firefox 17.0.1.