> Couldn't I just as well make the argument it's pretty annoying that Firefox doesn't implement the API features required for background blurring?
Maybe, if that were the case, though even the opacity of the messaging is also a problem. Not 'your browser doesn't support the XYZ API, which is required for this feature, try Chrome', or even 'your browser is unsupported, but if you want to try anyway, click here', but 'use a supported browser for this or fuck off <links to Chrome>'.
From what I've looked into on this in particular though, Google sends different code to Firefox, and does pretty aggressive browser detection to do so (spoofing UA is not sufficient to get the Chrome code), but if you can get it to run the Chrome code, it actually works fine. There may be some performance issues on Firefox that the Meet team doesn't like, but rather than doing an overrideable runtime performance check or exposing anything at all to the user, they just ban Firefox users from the feature. This is, if you ask me, totally against the principle of the web, which is meant to be based on open standards and running the same code everywhere, not deciding if you like the browser the user is using and giving them a degraded view.
We've seen where this leads before when we have a dominant browser vendor that wants to entrench that position, and now that vendor operates important web services too, which they can leverage to further cement that dominance. I don't think it is a good place to be.