Firefox on 9.04 won't play videos at YouTube

[Ken G.]

Recently there was a discussion of Firefox not playing videos on 
YouTube.  Here is a possible solution for playing elsewhere on other 
websites.

Solution [FOT004]:

Some video issues are caused by conflicting plug-ins. It's not a good 
idea to have multiple plug-ins for the same type of content.

To remove conflicting flash plug-ins and install only the one from Adobe 
open "Applications >> Accessories >> Terminal", then paste 
(CTRL+SHIFT+V) the code below in the terminal window and hit enter:

Code:

sudo apt-get remove swfdec-mozilla
sudo apt-get remove mozilla-plugin-gnash
sudo apt-get remove adobe-flashplugin
sudo apt-get remove flashplugin-nonfree
sudo apt-get install flashplugin-nonfree

Restart Firefox.

Quote:
Note: if you have only the plug-in from Adobe and can't watch videos 
only from certain web sites, then check if you have an extension like 
AdBlock. It might be blocking the content form the video. Replacing 
Adblock with AdBlock Plus might solve the problem. See discussion here.