They don't need to put incriminating "if Firefox" statements in their code -- the initial page request would have included the user agent and it would be trivial to serve different JavaScript based on what it said.

I’ve duplicated it on 4 machines across 3 OS’s (windows 11, macOS, steamOS). Glad you got lucky. I’m sure you’re also familiar with A/B testing but if not I’m happy to explain it.

It is absolutely possible there is a reasonable explanation but for you to say 1) nothing is happening and 2) it’s “bandwagoning” is, again, ridiculous. Especially if your evidence is “well mine is fine,” which is not acceptable troubleshooting procedure.

Not all regions are served with the same scripts. That's why the ad-block pop-up was shown for some users but not for others or at a later time for others. This also affected the update cycle of those anti-adblock scripts.

The reason for that is quite simple. New stuff is rolled out to only some users at first as some sort of beta testing procedure. If many people complain about functionality issues and all of those have the new version of the script, Google knows there is something wrong with it.

"works fine on my machine lol" is unhelpful and useless.

It's very well known that Google makes heavy use of a/b testing. They did it with the adblock block and they're doing it with this