Bug 833023 has been fixed as of yesterday for providing the VP9 decoding capabilities inside Firefox. Also fixed was Bug 918550 for having libvpx 1.3.0.
VP9 encoded video content with WebM can now be played from within the HTML5 video tag on future releases of Firefox. Google's Chrome web-browser has offered VP9 by default for several months. The VP9 video compression standard offers many improvements over VP8 to shine as Google's next-generation open video standard.
The VP9 support inside Mozilla Firefox will happen for the version 28 release.