Wether there is a formalized contract or not Mozilla makes choicses in the interest of Google over (especially power) users all the time. And in general its absurd to think that taking money (not to mention almost your entire funding) from someone isn't going to make you biased towards that person. As has been pointed out many times in discussions about this, you don't need any explicit deals for conflicts of interest to emerge. Having the wealth of Mozilla's leadership depend on Google's good graces is going to encourage them to make decisions that will keep Google happy.

Attacking users users that bring up grievances is not going to help your case here.

> There are some things Mozilla is disallowed from doing to Google Search results that Firefox displays, but that's basically it.

What exactly are those things? Is that why Firefox does not come with ad blocking by default?