Obviously there a people in charge now who will never understand the Streisand effect. They could have kept it quiet and just... allow... the technical adept users to do their thing. Now, they are the laughing stock and get unwanted attention. Also, from my layman understanding, this shit won't fly in the EU at all.
Or, to say it differently: This is the best thing to happen to Mozilla in quite a long time and I'm a fan.
Oh yeah, you shouldn't. But people do this for fingerprinting, bot detection, and other "adversarial" scenarios where you really don't like the person executing your code. It's somewhat plausible Google would use this technique to do something scummy like this (although that is not the case).
I'm guessing that it's a way for them to test if ads have been loaded after initial scripts have run, but I'm not going to dig into the code.
Honestly, the whole ads thing is missing the point. If you desired a public video hosting platform, that needs to be a tax-funded commons. Video hosting and streaming is very expensive. Similarly, users should be donating to keep Lemmy going: