Update RTCRtpSender.setParameters for Firefox (#3214)
Update RTCRtpSender.setParameters for Firefox (#3214)

* Update RTCRtpSender.setParameters for Firefox
This method was added in Firefox 46 and live-updating
of values was added in Firefox 64.

* Add descriptions to the methods so they appear correctly

chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data