Fix performance when LOTS (1200+) bins in history

This was causing the open/close panels to be /really/ slow, and I eventually figured out it was due to a large DOM hanging in the background. This should also fix scrollbar from partially appearing when the background history loads.
Merge pull request #831 from remy/fix/perf-issue-lots-of-bins

Fix performance when LOTS (1200+) bins in history