[Tracking Requested - why for this release]: original report: http://forums.mozillazine.org/viewtopic.php?p=14577953#p14577953 STR: Create new profile, launch it There will be two tabs already open - open a new tab and go to https://bugzilla.mozilla.org/show_bug.cgi?id=1058542 Click on this new tab and drag it between the other two tabs: [1][2][new tab] -> [1][new tab][2] Now click on the scroll thumb and drag it down in order to scroll the page. Make sure the mouse stays within the scroll bar for better results You'll notice that scroll bar is jumping up and down, that shouldn't happen. Regression window: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=0c1e74f83b4187dc5563b2fc4a64f19065132700&tochange=1d931aacb06118b0c182fea0d6d3d529b380cdb6 Regressed by: Bug 1242690

setting apz.drag.enabled = true seems to fix the problem

This might be the same issue as bug 1265806, but it might be different. Given the STR on this one I suspect bug 1260018 might fix it also. I'll take a look.

Yup, this one is fixed by bug 1260018.

Tested on m-i build. https://hg.mozilla.org/integration/mozilla-inbound/rev/746c21b668ac307976d6fb142f4b708146b58ee7 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:48.0) Gecko/20100101 Firefox/48.0 ID:20160420094343 Indeed, Bug 1260018 fixed this.