This could either be some of Firefox's privacy features genuinely making it look more bot-like to Google, Google accidentally or deliberately sabotaging Firefox, or some combination of the two. It's not really possible to tell from the outside, but it's clear that Google's incentives are for Google's products to work better with each other.

This is why Google should be broken up -- it should be forced to spin off Chrome into a separate company with a business model similar to what Firefox has.