Thanks for commenting. My comment was meant to to be slightly exagerated but since your response is grounded, I 'll rephrase mine too :)
The evangelist tweets (I won't dig them because it's not cool) are 100% real, but keep in mind they were meant to be humorous and not official stance.
Firefox 3 got released in 2008, but firefox 3.5 (arguably the best browser at the time) was released a year later. Mozilla released many firefox updates in the meantime I believe they did so even after firefox 4 was released (no forced update from 3.5 to 4).
Firefox 4 was delayed to my understanding due to the whole html5 hype and trying to support as many of the new standards as possible (this info is from twitter so it might be wrong).
Lots of projects in limbo, not much different than google pushing NaCl, Dart, webkit prefixes. It looks bad only when paired with the general low activity. There were some chat logs leaked of mozilla people talking about adding webkit prefix support to firefox. Some where getting very angry over this. Today firefox supports the webkit prefixes :p must have been a multi-year argument.
Lack of mp4 support was due to MPEG LA owning the rights to h264. Mozilla didn't wanna pay the patent owners, in the end cisco created openh264 and mozilla used that, in 2014 nonetheless.
Webm was not added because it wasn't a web standard. In my opinion both h264 and webm events got dealt in poor judgement but whatever.
The Yahoo change was due to an expensive multi-year contract between Mozilla and Yahoo. Money before users. I remember people defending it by saying that yahoo search is powered by Bing, not by yahoo themselves.
In general mozilla used to be this awesomely perceived company... no not company, foundation! They organized things like place giant firefox stickers in your city and gain online fame, and sending a cake to the IE team with every major release they did. Spearheaded the whole open web movement. It was Richard Stallman with Charisma 10! And then.. kinda suddenly stopped and became more like the Apache Foundation. Cool and all but slow and old.