Firefox has always been my favorite browser, with Chrome a close second, ever since it was released. I've found that Firefox is the better fit for both my needs and my tastes, its the browser where I feel more comfortable at.
Now, with the release of Firefox Quantum (aka 57) it has cemented its position. Not only I've found it actually a big step forward in terms of performance, I found that the user interface looks a lot better.
While the performance enhancements are really nice, and welcome, the new user interface is what I enjoy the most. One of my favorite tweaks is now I can get rid of the search box altogether, since I stopped using much once I was able to use the navigation box for internet addresses input and for search.
There is also the fact that now there are more options to personalization options to make Firefox look even more like you want it too.
With this release, Firefox has become a truly modern browser and a worthy contender.