In other words pretty much exactly what some tried to say when Google first launched Chrome, except for OSS zealots who were blinded by their Mozilla support and "do no evil" slogan.
For Google open source is not a goal, it's a tool. Google funded Mozilla to run a browser war by proxy, as an open source and non-profit organization Mozilla could get massive support from organizations and volunteers that Google never could and a much higher tolerance of bugs and broken functionality. And I mean that both with respect to internal bugs as well as broken web sites due to MSIE-only code. As a means to an end to push a standards compliant web for Google to profit from it was a success.
With Android Google again used open source as a battering ram against an entrenched monopoly, this time against Apple in smart phones. Once again a host of unlikely allies - pretty much everyone except Apple and Nokia, really - jumped on board along with the open source rah-rah and low cost clone manufacturers looking to get a free ride. That you could have things like CyanogenMod and get root on your phone was new - even though some manufacturers blocked that it was a step up from the all-closed platforms.
I'm not saying those are bad things, but those mutually beneficial interests come to an end. Once we've been released from the old stranglehold, Google wants to make a new one with themselves in control. I don't think I can make a catchy acronym for it like embrace-extend-extinguish but it goes something like commodify-bundle-obsolete:
1. Commodify the functionality through open source
2. Bundle it with Google APIs/services
3. Let the open source version toil in obsolescence
Search results are still a major driver of Google's revenue. The default search engine is defined by your browser, the default browser is defined by the platform so from their perspective pushing Android and Chrome both makes very much sense - if you're using a Google product you'll never be pointed anywhere but a Google service. Chrome is also a vital part of that "all-or-nothing" bundle Google is selling to make companies use Google Play which is now their second cash cow.
Firefox is no longer a partner against MSIE, they're a threat against the OHA bundle. If you can take AOSP and install Firefox with no further strings attached that's one of the many pieces you need to replace filled. The less alternatives you have, the more power Google has over the Android ecosystem. If you're still stuck in the mindset where MSIE had 95% market share you'll fail to see that your one-time ally is no longer on your team. They're on their own team, as every for-profit company eventually end up being.