Reproducible: always Steps To Reproduce: 1. Navigate several page in a tab. i.e, Navigates like New Tab > Site 1 > Site 2 > Site 3 > Site 4 2. Long mouse press back button, and then mouse up on 1st history(New Tab) 3. Long mouse press forward button, and then mouse up on history(Site 2 or 3 or 4) i.e, Mouse down on back/forward button and holding down mouse button so that session history dropdown will pop up. Continue holding down mouse button and then mouse up on a history entry. --- tab jumps to Site 1 instead select one, BUG!! 4. Long mouse press back button, and then mouse up on history(Site 1 or 2 or 3 or 4) --- tab jumps to New Tab instead select one, BUG!! Actual Results: Tab does not jump to the selected history. Expected Results: Tab should jump to selected history entry Regression window: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=f6eebcc14c22762f521fb567a9588963b8720592&tochange=61570c16c2d564c24fab36713fb169c4144453e9 Suspect: 36b949bef798 Olli Pettay — Bug 1089326, make <button> hit testing similar to other elements which may have some content, and for click target find the common (interactive) ancestor, r=masayuki

I'm pretty sure this is the same or similar issue to bug 1514791.

I confirmed that Bug 1514791 also fixed this. Fixed range: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=e4a0eaea412616e02e66ca6cc90d1f57a1b4d798&tochange=f256f0e01e82239fbdc7ec86e32a49a2ccc5b4d7