i'd like to have the questions i already visited to be highlighted so it would be easier to scroll thorugh them espcially when new ones are arriving.
how about it?
My browsers perfectly show the links I've visited, and I did not do anything fancy for that.
(Maybe you should set your browser to keep a longer history?)
You can use Greasemonkey or Stylish to change the a:visited links to something much more obnoxious if you like. I'm sure someone will come along with a script soon enough ;)