A SoC lifecycle can take 5 years to materialize in customer shipping hardware. Yet Mozilla is giving up before collecting the fruit of their previous policy (no system codec).
That's a shame.
The bigger issues are that
* Google never followed through on its declaration it would remove H.264 from Chrome, which would have made almost 50% of browsers that don't support H.264.
* Flash never followed through on its declaration it would include WebM, which would have enabled WebM in IE and Safari and made it possible for YouTube to go WebM-only (on desktop).
Mozilla using system H.264 codecs on mobile (not even desktop) doesn't matter at all compared to those.
Note that there are SoC already out there that support VP8/WebM. As far as I know Tegra 2 is one of them. What does it change? Nothing. All those chips support H264 as well. So H264 is what content producers use.