You don't remember what the original argumentation was. Firefox is free, Mozilla can't afford the patent licensing, that's all.
This is still entirely true (note that "afford" in the above should be read in the "free license" context, not monetary). For the same reason, Chromium has no H264 support. Patented codecs don't mix well with free software. They took a stance here based on their philosophy, that much should have been obvious.