I’ve just pushed a few patches to master that make some rather big changes to the way CodeMirror handles scrollbars. The effect for existing setups is intended to be nothing at all, and I’ve tried hard to add tests and guard against regressions, but I do recommend that you test scrolling behavior before upgrading critical sites.
The main purpose of this work is to allow custom scrollbar implementations. There is now an example of such a thing in this demo. As a bonus, it also allowed me to get rid of a few ugly kludges that worked around webkit scroll bugs.
So take a look whether this works for you, and if styling scrollbars was something you were waiting for, tell me whether the addon serves your need.