User-Agent strings are now net-negative in the web world. Their uses are slim, and their abuses are plentiful. They should probably be removed altogether, but in the meantime non-Chrome browsers should universally adopt Chrome's UA.
User-Agent strings are still useful for identifying non-browser user agents but I agree that given the privacy issues they present all browsers should adopt a single standard UA string (one each for desktop and mobile). (Did you know that Chrome on Android puts your device model in the UA string? One of the many reasons to use Firefox for Android...)
