Thanks for all of that. You're correct that the email I received from VDH refers only to a Firefox license. As it would turn out, however, said "Firefox" license worked in my Chrome browser but did not work in Firefox. (It's unclear to me whether this is because I tried using the license key in Chrome first.) I tested it out, and it's working fine in Chrome.
So now, the license is still not working for me in Firefox. Given your last message, I take it this is to be expected, as the license is only good for one browser. But I am confident that I've also taken out a separate license for Firefox... now how would I go about checking on that? When I first ran my email through the VDH database, it returns only the one "Firefox" license key.... which, quite curiously, only worked in Chrome lmao.
I've attached screenshots of the (redacted) email I got this morning with my license key, as well as the (redacted) pages showing the key worked in Chrome but not in Firefox.