Hello Linux Geeksters. As you may you Firefox has support for the H.264 format but unfortunately, the gstreamer0.10-ffmpeg package is not available by default on Ubuntu 14.04 Trusty Tahr, so H.264 videos are not natively supported.
So, for watching H.264 videos you will have to install FFmpeg plugin for GStreamer. In this article I was recommending the users to get download the gstreamer0.10-ffmpeg*.deb packages and install them via gdebi, but it looks like the gstreamer0.10-ffmpeg package is also available via some third party PPA, so installing it and enabling H.264 playback on Ubuntu 14.04 is quite easy.
All you have to do is add the ppa to your system, update the local repository index and install the gstreamero.10-ffmpeg package. Like this:
$ sudo add-apt-repository ppa:mc3man/trusty-media
$ sudo apt-get update
$ sudo apt-get install gstreamer0.10-ffmpeg