Free software. The Cisco H.264 codec supplied with Firefox cannot be distributed with other software, despite being "open". From https://www.openh264.org/ , there seem to be licensing costs involved with the usage of this code, which have been waived for some uses, implying they were not waived for others:

> We will not pass on our MPEG-LA licensing costs for this module, and based on the current licensing environment, this will effectively make H.264 free for use on supported platforms.

EDIT: To clarify, such licensing requirements on H.264 may make codecs fall outside of the guidelines of software distributions allowing only free software, making them supply their browser without one.

If I remember correctly, only decoding for online video streaming doesn't require licensing fees. Cisco hits the fee cap with the products they sell already, so letting everyone use their binaries doesn't cost them anything.

Right the core problem is you have to use their binaries so Mozilla can't build it and ship their own.

Also includes lots of people w/ custom Chromium-based browsers that don't ship with these codecs (and libs like CEF don't compile with them enabled by default).

Many RTC stacks (and specifically openh264) also only support H.264 baseline profile. So you are likely to get higher quality with VP8 (subject to variations in the quality of the implementations on each endpoint, of course).

Some services use WebRTC in a "hub and spoke" model rather than true peer-to-peer, and they often require VP8 due to a desire to support low-end Android devices that don't have hardware H.264 decoding.

I am surprised to hear that. Even $50 Android Phones now has H.264 hardware decoding support, what phones are those that doesn't come with it? And likely doesn't have VP8 hardware decoding either.