Bug 994185 - When dragging tiles on a 3x2 view, a third row of tiles shows up inexplicably [r=adw]
Also fixes Bug 988907 - Context menu and clicking-to-focus do not work in empty space above/below newtab grid
Cover up the sites that become position: absolute (and escape the flow for overflow: hidden) with an explicit background color for the bottom margin.
Merge m-c to fx-team.
Bug 988001 - Make the popup click to insert work again, r=bgrin
Bug 995027 logging - add traces to figure out whether uninit was called and where it got stuck, r=gfritzsche

--HG--
extra : rebase_source : 6c2e5dcce364bbce746a11b4e8841283656162c2
Bug 997188 - Handle the experiments.manifest.uri pref correctly so so that it don't ping out to telemetry-experiments.cdn.mozilla.net by default or enable experiment code in the tests. This should also fix bug 994686. r=irving/gfritzsche
Merge f-t to m-c