Enable the usage of Firefox for load testing

[atsakiridis]

Firefox doesn't have the restriction of https for webrtc yet, so it's much easier to test in non-dockerized environments, which are easier for testing

Some useful resources:

• On how to avoid user interaction on accepting the media popup: sadly this cannot be set via command line option as is the case with Chrome. We need to somehow alter the FF preference: media.navigator.permission.disabled and set it to true. The only way I found for that (to be used for automation) is by adding this preference via configuration file. See: http://askubuntu.com/questions/313483/how-do-i-change-firefoxs-aboutconfig-from-a-shell-script and https://mike.kaply.com/2012/03/15/customizing-firefox-default-preference-files/

[atsakiridis]

I managed to get it to work but I'm facing several issues:

• After spawning multiple FF windows from the script, FF seems to be keeping only one. To workaround that I added an interval between each window is started.
• Haven't found an automated way to set media.navigator.permission.disabled via script since preference must be updated
• Haven't found a way to access logs after run is finished. I asked on firefox-dev@mozilla.org still waiting for approval