Bug 1089621 - Add will-change: transform during edge-swipe. r=etienne
Bug 1089621 - Don't call _setActive in setVisibleForScreenReader. r=eitan

Calling _setActive will cause the browser element to repaint, which causes
jank during edge swiping.
Merge pull request #25622 from Cwiiis/bug1089621-janky-edge-gestures

Bug 1089621 - Improve janky edge gestures. r=etienne,eitan