Doesn't matter really. If you want to prolong the inevitable and/or run an unsupported o/s, or have to support esoteric software on the browser, use esr. Otherwise, pick the latest. I use the latest firefox on gnu/linux. I'll run it and hope for the best. If I don't like what they do, prolonging the pain for another year isn't that helpful. If you *require* a feature of old firefox, I'd run the portable version, and limit my general web use with it as it goes out of support.