This isn't about Google playing the good guy. Their core business heavily relies on big, personalized data. By giving all that money to Mozilla, they claim the default search engine and probably some other man-in-the-middle services too (like Google error pages or Google anti-malware protection). I haven't used Firefox for a while, but I guess that also includes auto completion in the navigation bar like Chromium.

It is only logical for them to invest in spots they can gain this data from.