https://tbpl.mozilla.org/php/getParsedLog.php?id=16639348&tree=Mozilla-Inbound Rev5 MacOSX Mountain Lion 10.8 mozilla-inbound opt test mochitest-1 on 2012-10-31 18:03:01 PDT for push 858e49a77dca slave: talos-mtnlion-r5-011 35586 INFO TEST-START | /tests/content/base/test/test_child_process_shutdown_message.html creating 1! [TabChild] SHOW (w,h)= (0, 0) loading http://example.org/, 1 XPCOM_MEM_BLOAT_LOG: /var/folders/md/gz7rkj9174dc03tkx5vb3w4400000w/T/tmpgcMJD2/runtests_leaks.log Writing to log: /var/folders/md/gz7rkj9174dc03tkx5vb3w4400000w/T/tmpgcMJD2/runtests_leaks_tab_pid839.log Security problem: Content process does not have `frobnaz' permission. It will be killed. 35587 INFO TEST-PASS | /tests/content/base/test/test_child_process_shutdown_message.html | Content child should not have this permission TEST-UNEXPECTED-FAIL | /tests/content/base/test/test_child_process_shutdown_message.html | Exited with code -20 during test run INFO | automation.py | Application ran for: 0:03:29.473591 INFO | automation.py | Reading PID log: /var/folders/md/gz7rkj9174dc03tkx5vb3w4400000w/T/tmpVCEDuUpidlog WARNING | automationutils.processLeakLog() | refcount logging is off, so leaks can't be detected! INFO | runtests.py | Running tests: end. program finished with exit code 236

Not quite sure, but I think https://tbpl.mozilla.org/php/getParsedLog.php?id=16903049&tree=Mozilla-Inbound is a worse flavor of the same thing, failing to be killed and instead sitting around until buildbot kills everything.

Fixed (or worked around) by bug 884471.