There is a difference between ensuring 100% support in major browsers, and applying a white list to usable browsers. Most of those small-time browsers are built

There is a difference between ensuring 100% support in major browsers, and applying a white list to usable browsers. Most of those small-time browsers are built on webkit, gecko or prestro anyway; so they shouldn't have any serious deviation of behaviour from the major browsers. Then you also have to consider javascript being a standard means most features should work on any browser that impelments the standard.