Bug 1524510 - Freeze quantum bar results when the user interacts with them. r=mak

Differential Revision: https://phabricator.services.mozilla.com/D25222

--HG--
extra : moz-landing-system : lando

browser/components/urlbar/UrlbarController.jsm

@@ -115,7 +115,8 @@ class UrlbarController {
    *   The reason the query was cancelled.
    */
   cancelQuery(reason) {
-    if (!this._lastQueryContext) {
+    if (!this._lastQueryContext ||
+        this._lastQueryContext._cancelled) {
       return;
     }
 
@@ -123,8 +124,8 @@ class UrlbarController {
     TelemetryStopwatch.cancel(TELEMETRY_6_FIRST_RESULTS, this._lastQueryContext);
 
     this.manager.cancelQuery(this._lastQueryContext);
+    this._lastQueryContext._cancelled = true;
     this._notify("onQueryCancelled", this._lastQueryContext);
-    delete this._lastQueryContext;
 
     if (reason == UrlbarUtils.CANCEL_REASON.BLUR &&
         ExtensionSearchHandler.hasActiveInputSession()) {

browser/components/urlbar/UrlbarView.jsm

@@ -36,8 +36,8 @@ class UrlbarView {
     this._mainContainer = this.panel.querySelector(".urlbarView-body-inner");
     this._rows = this.panel.querySelector("#urlbarView-results");
 
-    this._rows.addEventListener("mouseup", this);
     this._rows.addEventListener("mousedown", this);
+    this._rows.addEventListener("mouseup", this);
 
     // For the horizontal fade-out effect, set the overflow attribute on result
     // rows when they overflow.
@@ -140,6 +140,9 @@ class UrlbarView {
       throw new Error("UrlbarView: Cannot select an item if the view isn't open.");
     }
 
+    // Freeze results as the user is interacting with them.
+    this.controller.cancelQuery();
+
     let row = this._selected;
 
     if (!row) {