I doubt it’s malice as often as a cost saving measure presented in a scummy/lazy way.
The simple fact is that all browsers load pages differently.
If you want to minimise cost, you’ll optimise the site to the most popular browsers.
Firefox, unfortunately, is at the very bottom of the popular browser list.

There’s absolutely nothing else that most sites gain by promoting Google.
Except, as of recent, a lower likelihood of user having an ad blocker.