This amazes me. Thanks for your honesty, there are probably millions of people who are in the same position. While you're looking down, wouldn't hurt to look at all the different keys and give them a try.
Turns out the f12 key was the culprit; took me longer than it should have to realize she was describing the Firefox developer console.
Push, push-and-hold, and push multiple times quickly.
TIL Enter key toggles comment collapsing.