I'm not about to speak to the intent of programmers I haven't interacted with heavily. In these sorts of charged conversations there is often an impulse to make issues about "this" or "that" exclusively. I find it useful to avoid that impulse entirely and instead focus on what I can do to make things better.

Well then let me restate my question. Are there regressions in Firefox that hinder performance on Google properties?

Not stating Google is intentionally slowing down things - but I've noticed that Google products and only Google products are slow to render, slow to click into the search field of Google Maps, and when I press 'compose' within Gmail on a macbook pro 2017 I can wait easilly 10 seconds before the email bit pops up. Within Chrome however, quick and slick.

Google has a history of disabling or degrading features (image search, maps, youtube) in browsers that aren't Chrome under the "we haven't fully tested them" excuse. In almost all cases changing your user agent to Chrome would result in a perfectly functional site. Perhaps there is 1 feature that didn't work but it was usually obscure and it feels like Google was just throwing the baby out with the bathwater to spite anyone not using Chrome. Up until recently it felt like Google made a Chrome version of their product and a lowest common denominator version and anyone that isn't using Chrome got the later. Now it seems like they let some browsers use the Chrome version but there are unusual performance regressions compared to Chrome. It's very reminiscent of the first browser wars where sites were IE or Netscape only.

The whole point of standards push over the years was so that developers could just code to the standard and the browsers would either catch up or suffer the consequences. It seems like these days Google is dipping into Microsoft's old playbook for every trick it can find to get people to switch to Chrome.