[Dev] Recommendations to avoid WebRTC leak in Iceweasel/Icecat

[bill-auger]

i want to add that the 'iceweasel-hardenend-preference' package
exists for this very reason: to put the browser default settings
into the most strict state for privacy - we just need to ensure
that the 'iceweasel-hardenend-preference' package disables the
webrtc leak; then we would only need to recommend installing
that, to disable webrtc

if it is not possible for the 'iceweasel-hardenend-preference'
package to disable the webrtc leak, then we would need to build
a separate iceweasel for the privacy repo