+++ This bug was initially created as a clone of Bug #1332708 +++ In bug 1332708 the following failures were reported: TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testAnnualRecurrence.js | testAnnualRecurrence.js::testAnnualRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testBiweeklyRecurrence.js | testBiweeklyRecurrence.js::testBiweeklyRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testDailyRecurrence.js | testDailyRecurrence.js::testDailyRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testLastDayOfMonthRecurrence.js | testLastDayOfMonthRecurrence.js::testLastDayOfMonthRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testWeeklyNRecurrence.js | testWeeklyNRecurrence.js::testWeeklyNRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testWeeklyUntilRecurrence.js | testWeeklyUntilRecurrence.js::testWeeklyUntilRecurrence TEST-UNEXPECTED-FAIL | C:\slave\test\build\tests\mozmill\cal-recurrence\testWeeklyWithExceptionRecurrence.js | testWeeklyWithExceptionRecurrence.js::testWeeklyWithExceptionRecurrence With bug 1332708 now landed, we're still seeing them intermittently: https://treeherder.mozilla.org/#/jobs?repo=comm-central&revision=f469e0a1b35e13268d0a8ed06240cc364258a5f0&selectedJob=72810632 TEST-UNEXPECTED-FAIL | /builds/slave/test/build/tests/mozmill/cal-recurrence/testWeeklyWithExceptionRecurrence.js | testWeeklyWithExceptionRecurrence.js::testWeeklyWithExceptionRecurrence TEST-UNEXPECTED-FAIL | /builds/slave/test/build/tests/mozmill/cal-recurrence/testWeeklyUntilRecurrence.js | testWeeklyUntilRecurrence.js::testWeeklyUntilRecurrence and https://treeherder.mozilla.org/#/jobs?repo=try-comm-central&revision=531fc1f6b72d417a98235d11a54a058ec9227fd5&selectedJob=72805818 TEST-UNEXPECTED-FAIL | /builds/slave/test/build/tests/mozmill/cal-recurrence/testLastDayOfMonthRecurrence.js | testLastDayOfMonthRecurrence.js::testLastDayOfMonthRecurrence MMD mentioned in bug 1332708 comment #4 that some of those were known from bug 980515. Now I think it's time to look at them. Also see attachment 8829201 [details] [diff] [review] of bug 1332708 for a suggestion to where the problem *may* be. Also read bug 1332708 comment #46.