How do you account for them directly supporting GIF? I'm not disagreeing in principle; but history shows that Mozilla as an organization is capable of picking it's battles and even supporting patent encumbered formats if doing so will make the Web a better place.
Being an employee of a one of the largest online video providers, I can assure you that both we and our customers see multiple encoding formats as a big deal.
GIF is a different situation. It was already a well established format before Unisys started enforcing the patent it held on it. The patent was a "submarine" patent, so it was not publically known before the format became widely used. It's also worth pointing out that the GIF fiasco was well underway (1993-1999) before Mozilla ever existed. The Mozilla organization formed in 1998, and was mostly influenced by the vast number of participating Netscape employees until 2002-2003. By 2003 Unisys's patent had expired.
If anything, Mozilla's stance towards H.264 is an attempt to avoid the web ending up in a similar situation it did with GIF, where the format was deeply entrenched before the companies controlling the licensing began asking users to pay license fees. The MPEG-LA's recent announcement that internet streaming would remain free until 2015 is a direct attempt to achieve further entrenchment of the format. There is a very real possibility that they will ask for licensing fees come 2015. And we have no idea how much they might cost. Even with free streaming, most of the people in the video production chain need to pay license fees to the MPEG-LA right now.
The GIF patents expired while Firefox was still in early development. And it was not the GIF format itself which was patented, but a particular compression algorithm used with it -- decoders, as used in Mozilla, were not patented.
People could (and did) create uncompressed GIFs to avoid the patent risk. For obvious reasons, uncompressed H.264 is not useful.
Being an employee of a one of the largest online video providers, I can assure you that both we and our customers see multiple encoding formats as a big deal.