Sound Flower captures OS sounds, but not browser's audio

I was trying to capture audio of a webinar and Quicktime was capturing the OS audio as expected, but for whatever reason it was not picking up the audio from Firefox.  I decided that maybe it was a browser thing and I was right.  Logged in to the webinar with Safari and it worked perfectly.

Download Sound Flower before trying to record.

Download, install, and then open.  Once open, you will have a little icon at the top of the screen.  Select Sound Flower 2 Channel, Built In Output.

Open Quicktime

File -> New Screen Recording

On the upside down triangle, select Sound Flower 2 Channel

Start Recording!