He's referring to Firefox browser and click F12 opens console within browser itself to do this stuff he's asking.
Yes, I realize Alexander Ebert is referring to the Browser I use (which is Firefox).
But what was stated in the instructions from Alexander Ebert is:
AFTER clicking on F12 I am supposed to locate the tab labelled Console; then paste the following line into the input field ....
HOWEVER, WHERE is there such a TAB LABELLED CONSOLE???
I was not able to locate the "tab" mentioned.
Perhaps this "tab" is also called something else on the computer I use???