Yes, this started after bug 980231 landed. 11:31:25 INFO - 452 INFO TEST-START | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js 11:31:25 INFO - 453 INFO checking window state 11:31:25 INFO - 454 INFO TEST-PASS | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | selected tab has the current timestamp 11:31:25 INFO - 455 INFO TEST-PASS | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | new tab hasn't been selected so far 11:31:25 INFO - 456 INFO TEST-PASS | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | new tab has the current timestamp after being selected 11:31:25 INFO - 457 INFO TEST-PASS | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | original tab has old timestamp after being deselected 11:31:25 INFO - 458 INFO TEST-UNEXPECTED-FAIL | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | new tab has the current timestamp since it's still selected - Got 1417030285487, expected 1417030285488 11:31:25 INFO - Stack trace: 11:31:25 INFO - chrome://mochikit/content/browser-test.js:test_is:834 11:31:25 INFO - chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js:step4:30 11:31:25 INFO - null:null:0 11:31:25 INFO - 459 INFO TEST-OK | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | took 442ms

309 INFO TEST-UNEXPECTED-FAIL | chrome://mochitests/content/browser/browser/base/content/test/general/browser_lastAccessedTab.js | selected tab has the current timestamp (difference: 3) - (from comment 12) This is post-patch. Should we increase the fuzz treshold to something more like 10?

I just decreased the delay between the steps to 10ms (bug 980231 comment 19), so a 10ms tolerance would be too much and not reliably catch a regression. I've increased the tolerance to 5 for now: https://hg.mozilla.org/integration/fx-team/rev/6283ef6b1257 If this is not enough, both the tolerance and the delay will need to be increased.

increased the tolerance from 5 to 15: https://hg.mozilla.org/integration/fx-team/rev/f46dc1e8d238

Apparently this bug wasn't updated when the patch was merged to mozilla-central. http://hg.mozilla.org/mozilla-central/rev/f46dc1e8d238