finding the mpegdash file or HLS link and piping that through ffmpeg usually works. though I am not sure if bigcmen has some encryption for their vids - I know that JFF/OFF content is encrypted and harder to download without additional tools.
for extension I can recommend https://addons.mozilla.org/en-US/firefox/addon/live-stream-downloader/ its good for sniffing out those links it can also download them without issues (will resort to copying the URL into ffmpeg if it doesnt download)
if the video you are downloading ends up looking garbled then its using encryption and it wont work