Install mplayer to enable video under Firefox

Mplayer download page Instructions for installing mplayer using yum

Here is what I ended up doing the second time, when it actually worked. Note that
installing mplayer-codecs pulls in mplayer and xvid rpms.
Also, I had to download and install mplayer mozilla plugin rpm separately.

$ sudo yum install mplayer-codecs
$ sudo yum install mplayer-codecs-extra