H.264
"and you can mix MPL code with proprietary code to form a single executable"
I'm sure that you will find that this 'update' is simply modifying their license so that they can include support for H.264 with Firefox.
http://weblogs.mozillazine.org/roc/archives/2010/01/video_freedom_a.html
"It is possible to obtain patent licenses in a way which works around the letter of the GPLv2 and LGPLv2, but honoring the letter while violating the spirit is not a game we are interested in playing."
With Google going full steam ahead using H.264 for Youtube+HTML5 Mozilla clearly don't want to be the only browser out there not supporting it and if you read the section "Mozilla should pick up and use H.264 codecs that are already installed on the user's system." from the article linked above you'll see their need for proprietary code bundling ;)


