>>> 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 (middle button) on parent doc [to start autoscrolling parent doc] 5. move mouse to the link in <iframe> 6. mouseup on the link [to finish autoscrolling] Result: The link was clicked Expectations: It shouldn't happen, because A) mousedown (4) and mouseup (6) targets aren't the same node B) it's an unwanted action in the middle of autoscrolling 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. If you can't reproduce this on Windows, there must be a misunderstanding. Do request a screencast.