Last time I checked pretty much all the money Firefox earns is paid by Google and if you see them in that kind of relationship, all the bad decisions that made Firefox worse with every new version since the release of Chrome make a lot more sense.
I've also wondered why they remove certain features that draw people to Firefox. I still think it's the better browser in terms of a browsing experience, but it's losing that edge by trying to become like Chrome.
And yeah, you're right; it does make a lot of sense.