How much does/did Mozilla pay for mp3 licensing?

Is it possible to find out how much Mozilla pays to allow firefox to have mp3 support? Is that public info?

Note: I hope not to get into a debate about licensing politics. Just looking for info.

Firefox relies on libraries supplied by the platform for MPEG decoding (such as Media Foundation on Windows, or FFmpeg on Linux). So I think the answer is $0, but someone else might have more info than I do.