Firefox 46.0 has two flags called --recording and --recording-output. I've searched the net and nothing was said about them. Also I tried it myself - didn't notice a change.
What does firefox --recording-output  do?
firefox
Those flags introduce a new feature in Firefox which allows users to record web pages drawing for debugging purposes using Microsoft Azure. The drawing could include bitmaps drawn, and all font true-type data etc. These information in form of traces, could help in measuring performance and fixing bugs across Azure back-ends.See Presenting the Azure Drawing Recorder, Add ability to record azure page drawingand Application Architecture on Microsoft Azurefor more info.Note that this is currently only available in Microsoft platforms.