Merge fx-team to m-c a=merge

Merge m-i to m-c, a=merge

Back out 6 changesets (bug 1290116) for a 70% chance of WinXP debug timing out in test_subscription_change.html

Back out 89c4afd55323 (bug 1291833) for causing "TypeError: gWebRTCUI is undefined" in browser_devices_get_user_media.js

Bug 334598 - Use Unicode symbols in print preview page navigation buttons. r=felipe

Bug 1168260 - Test: Promise methods should not be enumerable. r=till

Bug 1237762 - Test: Promise resolved with itself rejects.r=till

Bug 940872 - Make library window draggable by toolbar on Linux. r=dao

Bug 1198648 - Status bar should obey high-contrast theme. r=mconley

Backed out changeset 6a5f939e29de (wrong patch)

Bug 1283126 - wasm: Take alignment hints into account when compiling load/store (r=sunfish)

Bug 1267365 - move various flags out of DevToolsUtils and don't depend on that module so much r=tromey

Bug 1263011: Part 2 - Implement WebExtensions Experiments prototype. r=aswan

Merge m-c to fx-team, a=merge

Backed out 2 changesets (bug 1258539) for winxp pgo talos g2 permafail a=backout CLOSED TREE