I'm a volunteer and order don't take my word for it but I think it's fine as long as you are not violating municipal, provincial/state and/ or federal laws of you who is recording and the other party as Mozilla is committed to being open and is fighting to keep the web open. However, I will escalate to the support help desk we have.. Please stay tuned.
And btw, only 4 % of the world lives in the US :-P And another 1,5 % in Mexico. The rest of us just have a single legislative organ, and in most places it's your right to record your own calls. I appreciate your help! I'm just frustrated at mobile phone companies handicapping their product, because of weird pratices in a tiny market share.
Thank you for your question, I have asked the engineers about this and will get back to you as soon as I can.
It looks like currently this is not possible because there is no api that exists for this yet. However, currently I found the media stream capture in version 1.2+ and has to have the apps permission referred to here: https://developer.mozilla.org/en-US/A.../Reference