Happened on Mac OS X 10.6.8, with Firefox 28.0a2 "an" locale (build id: 20131217004003) http://mozmill-crowd.blargon7.com/#/functional/report/ca1869364f98dd0de71202e01ee04b25 Reproduced locally. Did not reproduce with Firefox 27.0 beta 2 (20131216183647) or with other locale (e.g. xh)
This fail occurs because the test /testPrivateBrowsing/testOpenClosePBKeyboardShortcut.js previously fails - bug 951208. This test doesn't fail anymore if /testPrivateBrowsing/testOpenClosePBKeyboardShortcut.js is removed from the testrun.
This test seems to work as expected since the shortcuts for pb mode are working. Fixed via bug 951208.