Last modified: 2014-03-07 11:44:12 UTC
mw.webfonts.setup takes 3 seconds on Special:ManageMessageGroups when it displays 1000 diffs. I believe the number dom nodes with a class makes it very slow.
Set this to impact minor for now. Are there indications that a large number of very often referenced pages are also affected? That might increase the impact.
The page was unusable before I implemented the limit to only show 1000 diffs. Now it's only annoying.