Mozilla (Firefox) management thought that installing a Mr Robot advert extension on people's computers, without asking, was a good move, and defended it until the internet outcry got loud enough. With management like that, I find it hard to trust them. Default-installing Pocket was also not entirely defensible and was probably money-driven.

Essentially, both companies have done anti-privacy and untrustworthy actions, and choosing the lesser evil is hardly ideal.

The difference between Mozilla and Google is substantial. Whenever Mozilla gets this wrong it is usually a goof of sorts, when Google gets it wrong it tends to be policy. See 'AMP'.