It is impossible for me to open the browser toolbox on my new factory-fresh macbook.
This video showing how it’s done, https://youtu.be/HMozipAjrYA, has a popup window asking to allow for incoming connections. No such window appears for me.
I just wait five seconds, only for a blank screen that says
Error opening Browser Toolbox:
Component returned failure code: 0x804b000e (NS_ERROR_NET_TIMEOUT) [nsIInputStream.available]
My firewall is off.
SOLUTION: Restarting Firefox didn’t fix it, but restarting my computer did.