I don't use Firefox because it's slower than Chrome and because their behavior regarding limiting which extensions are available in phones, requiring signed extensions, Firefox Pocket, ads in new tab page, etc, does not exactly give me confidence that Mozilla truly has my interests in mind. In fact I bet they'll implement the nightmare DRM API once it's done swiftly and without complaint lest their money flow suffer.
If Mozilla ever decides to stop screwing around, clearly position themselves as an ally of the consumer, clearly express support for adblockers and put resources into making the browser faster and better and more customizable instead of whatever makes their CEO richer then I'll switch to Firefox even if it is a bit slower or has some flaws.
In the meantime uBlock works right now in Chrome which makes it usable, so since Chrome is the fastest right now, Chrome it is.