I was a bit frustrated by the GitHub UI trimming file names too short for them to be uniquely identified. See this screenshot (I was looking for was ChangeMessageVisibilityBatchResponse.cs).
There is a lot of wasted screen real estate in the left and right margins that could be better used to display more of the file names. I already use a Chrome extension called Stylish to customise website CSS and went to setup custom styles to solve this.
First I checked for any existing styles and found Wide GitHub custom styles created by mdo. This was a great starting point, it makes GitHub fluid. To this I added some additional CSS to remove the widths set on the filename and message columns. This causes the columns width to change from page to page as the browser will recalculate the width based on the contents of the columns, but I think this is preferable to cutting off content.
My changes are available here and I have submitted them as a PR to Wide GitHub.
Finally here is the screenshot of the UI after the changes.