http://zqktlwk5ilgohy63eyrptyb4mc76bunfmxcnstkmveyjnskxkpq3b5yd.onion/wiki/Network_Attributes_Of_Your_Computer
MAC addresses do not cross router boundaries, so anything outside of your LAN will never see it. If your adversary is not internal to the LAN or cannot trace your IP address back to the LAN, don't worry about your MAC.