Manifestos are about principles not pragmatic approaches, taking a stance is not free or easy, look at the stance RMS takes on open source and GPL for example. Had RMS and other pioneers in the open source movement did not take such ideologically driven stance at the expense of pragmatism , we may have parts of BSD maybe today but not the GPL driven open source ecosystem that all of us benefit from, even now it costs open source a lot look at linux and zFS .
You can apply the same argument with Google early on, they were hugely influential in reducing the amount and type of ads we were forced to see. They have developed great open source projects and provided a lot of good quality free services all funded by ad revenue, how is it really different from Mozilla then ? so should I see only those contributions and ignore what Google really does on privacy ?
Being uncompromising in the face of great difficulty is the only way of real, sustainable change and revolutionize how things work, had Google stuck to "Do no Evil"(whatever that meant to them) no one would worry about using Chrome, if organizations loose focus they only really exist to make money for employees/ shareholders/ management.
Also this is not sustainable model, that search revenue is going to keep dropping as they keep loosing market share, inevitably they are either going to drop Firefox altogether or going to base it of Chrome and shelve most of the team. If Microsoft cannot afford to develop Edge as separate browser, how long Firefox will last in this structure ?
We are better off forking off in a community funded model before the inevitable happens and try to build a sustainable project around that. There are enough companies who can donate few million dollars a year each to make sure Google is not the only player in town. Wikipedia raises more than $120 M / year, it is not inconceivable, that Moz foundation can raise a reasonable amount to fund the development of the key projects.