The bullet point about the plugin rendering fix on Mac OS X closes the list item twice instead of closing the link. (That is, it has </li> where it should have </a>.) Also, the usage of for "Firefox 4 (Beta)" is inconsistent throughout.
All of them say Firefox 4 beta now. Committed at r74549.
Verified FIXED on trunk: http://html5.validator.nu/?doc=http%3A%2F%2Fwww-trunk.stage.mozilla.com%2Fen-US%2Ffirefox%2F4.0b6%2Freleasenotes%2F.
r75796 on prod
verified fixed on production http://www.mozilla.com/en-US/firefox/4.0b6/releasenotes/