Since we updated Firefox on Jenkins, one specific unit test fails every time:

However, locally this is difficult to reproduce, and Travis never seems to hit the bug.

Some observations:

• The test uses defineProperty on option elements at these lines:

  angular.js/test/ng/directive/ngOptionsSpec.js

  Lines 2903 to 2906 in 9bcdfcf

  	Object.defineProperty(option, 'selected', {
  	get: function() { return _selected[i]; },
  	set: optionsSetSelected[i].and.callFake(function(value) { _selected[i] = value; })
  	});

  . When the test fails, the redefined setter / getters is never called
  (We also use defineProperty on other tests that don't fail, but none on option elements)
• it seems to happen more frequently when the FF window is unfocused and when the CPU usage is very high.
• Firefox runs the tests much slower than e.g. Chrome, and seems to "hang" at certain points for a few seconds
• The failure could not be reproduced when the test is isolated with fit.
• The failure is not dependent on the jasmine.spy
• happens less frequently in FF53

Possible causes:

• Electrolysis. Activated since FF47 by default iirc