Oh Snap!s when hovering PR diffs

Performance on PR page is killing my tabs. Namely this guy https://bitbucket.org/atlassian/aui/pull-request/528/implement-jshint/diff seems really slow.

I think it has to do with hover styles, but I'm not sure. Seems fine until my mouse goes over a diff, then I get a long freeze and a dead tab.

Chrome Stable on Windows.