Phoronix reader "RussianNeuroMancer" tipped us off today about LaunchPad Bug 1275556. This issue is about the "gstreamer0.10-ffmpeg" package not being present in the Ubuntu 14.04 archive. This package serves as the FFmpeg plug-in to GStreamer 0.10. The gstreamer0.10-ffmpeg package has been found in older Ubuntu Linux releases but is not part of the 14.04 LTS archive.
Besides Firefox H.264 support not working without this package, KDE applications with the Phonon GStreamer back-end (among other apps) will not support H.264 content. Fortunately, this support can still be found through external PPAs or compiling the code from source, but that's not too great for the Ubuntu 14.04 LTS experience for those wishing to play H.264 content with ease.