A note here - this isn't just about privacy, but also about usability.
The problem is that many times I can remember an article I've read or a link I visited only vaguely, by a single word in the title or something like that. Well, try searching for a single word on Google.
For example, I tried typing "manifesto". Firefox's Awesome Bar suggested to me amongst others: a YouTube video called "Firefox Manifesto 2012" (watched it yesterday), a blog article on a website titled "The Social Customer Manifesto" and a link to ReactiveManifesto.org.
I typed the same in Chrome and note that I keep Chrome around and it has a very rich history. Guess what Chrome gave me? Nothing from my history. It only gave me search suggestions like "manifesto definition", "manifesto lyrics" and "manifesto of the communist party".
So that's a big problem. You remember a single word or two. You want something from your history. Firefox does a good job at suggesting from my history. Chrome expects me to do searches on Google. I wouldn't mind those searches, but they aren't solving my problem.
So yes, that's why Firefox is back again to being the browser I love most. Along with Tab Groups and efficient UI tweaks that I can do, I find it hard to use anything else.