Security and privacy isn't only prevalent on browser frontend features. There are battles happening within every standardized Web specification. Without more than one major player, one company would be allowed to dictate the level of security and private within every API. There are also initiatives that push the Web forward in security like with Let's Encrypt or Do Not Track. Mozilla also advances into new areas of technology to try to ensure they remain open.
It's totally fine to prefer one browser or the other. It's great to have an actual choice. But the ideals and values aren't just for show.
Ideas and values don't matter if you don't have enough power to make a difference in the world.
What has Mozilla actually done in the past few years to push the web forward in security or ensure that a web specification protects user freedom?
Things that Microsoft or Google or Apple were also trying to do don't count -- what good things did Mozilla succeed in doing that the other browser companies opposed?
But it is now 2017, and when I decide which browser I should use, I choose one that is good today, and I don't care about the blows its parent company struck for or against freedom 13 years ago.
I also disagree with the assertion that Firefox is better for security or privacy than Chrome is. They are comparable in their security and privacy features.