>>> My Info: Win7_64, Nightly 46, 32bit, ID 20160105030211 Basic STR here is: 1. mousedown on a link in <iframe> 2. move mouse to parent doc 3. mouseup on parent doc 4. mousedown on parent doc 5. move mouse to the link in <iframe> 6. mouseup on the link Result: The link was clicked Expectations: It shouldn't happen, because mousedown (4) and mouseup (6) targets aren't the same node Notes: See self-explanatory "testcase 1" and "testcase 2" for detailed STR IE11 and Chrome do not expose this bug. Though IE doesn't support "data:" links, so "testcase 2" with Google Analytics was made for IE11. Also, "the button" was also made for IE11 and Chrome, because otherwise they usually try text selection and don't even fire mouseup on the link from Step 6 above. If you can't reproduce this on Windows, there must be a misunderstanding. Do request a screencast.