import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 1240985 - Always enqueue OnMaybeDequeueOne task when receiving a message (r=dvander) (a5056d5942)
- Bug 1240985 - Null out mRecvd if message it corresponds to is cancelled (r=dvander) (3eb16e50b4)
- Bug 1245649: Merge browser and toolkit eslint rule settings. r=felipe (fb8837edb9)
- Bug 1189799 - Make sure that about:performance displays each add-on only once (more tests);r=felipe (67cc74db67)
- Bug 1230471 - Basic eslint fixes in places. r=mconley (1460c46edc)
- Bug 1142734: Allow unloading the loader sandbox module. r=jsantell (052f483a6d)
- Bug 1047595 - make picking colors work in HCM / when author colors are disabled, r=jaws (728163434b)
- Bug 1244647 fix typeof check, r=mikedeboer (72da15da21)
- Bug 1229240 - make applyConstraints() reject instead of crash on non-gUM tracks. r=jesup (93d2abf43a)
- Bug 1239893 - Add gonk SidebandStream handling to DOMHwMediaStream r=roc (86739bc7a4)
- Bug 1189162 - Clamp gamepad.timestamp and VideoPlaybackQuality.creationTime. r=bz (daaa3cc0db)
- Bug 1232348 - adjust nested-frame checking condition. r=baku. (e4d1930bef)
- Bug 1166556 - Don't start geolocation provider if the cached position is being used. r=jdm (3ad2c5dfa9)
- Bug 858827 - [Geolocation] Add a handling for getCurrentLocation when timeout is zero. r=jdm (63dd4ccaf3)
- Bug 1216148 - Handle how geolocation acts when the app's visibility changes. r=kchen. (dbeb9ef51c)
- Bug 1230209 - Add more telemetry for Geolocation usage f=bsmedberg r=tanvi,rbarnes,jdm (c32b195d25)
- Bug 1238825: Add "dom.bluetooth.webbluetooth.enabled" preference for WebBluetooth API development. r=btian, r=bz (3298be0b87)
- Bug 1223722: Transfer Bluetooth addresses in |BluetoothValue|, r=brsun (1cc507823b)
- Bug 1223722: Transfer Bluetooth remote names in |BluetoothValue|, r=brsun (73a008b991)
- Bug 789315, notify MutationObservers before running <script>, r=khuey (d2df797c54)
- Bug 1214495 - Move CallerSubsumes checks in nsLocation into the WebIDL entry points. r=bz (69a2086836)
- Bug 1239509: Move VisibilityChangeListener out of nsContentPermissionHelper's header. r=wchen (bb2e33a40c)
- Bug 1183845 - Only send activation event if document is non-null. r=bz (4b81c3295d)
- Bug 1208789, clear starting node before traversing backwards by document, r=smaug (94a6cdd891)
- Bug 1240908 - Make the window reference in nsContentPermissionRequester weak. r=smaug (b5982ecb9e)
- Bug 1234735 - Remove redundant spaces in nsGlobalWindow. r=baku (5f55b37486)
- Bug 1180525. Run callbacks whose window is no longer current as long as its document is the active document in the browsing context. r=bholley (02e6d97a7b)

dom/base/nsScriptLoader.cpp

@@ -962,6 +962,11 @@ nsScriptLoader::ProcessRequest(nsScriptLoadRequest* aRequest)
   // The window may have gone away by this point, in which case there's no point
   // in trying to run the script.
   nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
+  {
+    // Try to perform a microtask checkpoint
+    nsAutoMicroTask mt;
+  }
+
   nsPIDOMWindow *pwin = master->GetInnerWindow();
   bool runScript = !!pwin;
   if (runScript) {