fixed the firefox 13+ smooth scrolling bug

Since Firefox 13 "smooth scrolling" is enabled by default and there's a problem with slow scrolling at long lists or grids. If you visit the excample page at http://addepar.github.com/ember-table/ with a firefox and "smooth scrolling" activated, the scrolling gets extremely slow and just moves by 1px.

When you disable "smooth scrolling" under "tools > options > advanced > general" everything works fine. But since FF 13 the option is enabled by default. The problem seems to relate to the event object provided by mozilla.

This fix is everything but good and I would be happy if someone has a better idea. I will further look into it, as Im sure theres a much better solution.