Codecs are compression-decompression algorithms.
Spot the MPEG LA members.
Note 1: There is another codec - Ogg/Theora (OGV), it has similar support to WebM but Android does not support it. Only Firefox 3.5 supports OGV and not WebM
Note 2: Most mobile browsers support whatever the underlying OS does. This is what desktop Firefox will do going forward.
Note 3: Similar situation with audio between mp3 and Ogg Vorbis