In the past we decided to support desktop Chrome, FF, Safari current - 1. This should still be fine.

As for Mobile Browsers, the same is probably true for Safari, and Chrome and FF for android. Chrome for iOS is essentially a WebView so that has the limitations of Safari on iOS.

For the stock android browser, we should probably be in line with the Android libs, and support 4.1 and up

As for IE, i think that we should looking forward and target 10/11 and up and Spartan