If you're looking for an abstraction, GWT can do a lot of things for you. It still supports IE6, so it often includes a workaround - sometimes JavaScript based - for that browser. As long as you use GWT widgets and layouts, this happens automatically, so you don't have to make changes to your code for IE6. (Of course, it can't do things that are impossible in IE6.)
You would have to be willing to make the jump to GWT's programming paradigm of course (which I personally find great, but that depends mostly on the question, if you like Java or not). However, you can use gwtquery to write a lot of the code in JQuery style (pretty much the same syntax and it's even a bit faster).
