Bug 860779 - Enable two-finger horizontal swipes when swipe animations are disabled. r=smichaud

browser/base/content/browser-gestureSupport.js

@@ -177,7 +177,7 @@ let gGestureSupport = {
    *        The swipe gesture start event.
    */
   _setupSwipeGesture: function GS__setupSwipeGesture(aEvent) {
-    if (!this._swipeNavigatesHistory(aEvent) || !gHistorySwipeAnimation.active)
+    if (!this._swipeNavigatesHistory(aEvent))
       return;
 
     let canGoBack = gHistorySwipeAnimation.canGoBack();
@@ -534,15 +534,10 @@ let gHistorySwipeAnimation = {
    * by the platform/configuration.
    */
   init: function HSA_init() {
-    if (!this._isSupported() || this._getMaxSnapshots() < 1)
+    if (!this._isSupported())
       return;
 
-    gBrowser.addEventListener("pagehide", this, false);
-    gBrowser.addEventListener("pageshow", this, false);
-    gBrowser.addEventListener("popstate", this, false);
-    gBrowser.tabContainer.addEventListener("TabClose", this, false);
-
-    this.active = true;
+    this.active = false;
     this.isLTR = document.documentElement.mozMatchesSelector(
                                             ":-moz-locale-dir(ltr)");
     this._trackedSnapshots = [];
@@ -550,6 +545,16 @@ let gHistorySwipeAnimation = {
     this._boxWidth = -1;
     this._maxSnapshots = this._getMaxSnapshots();
     this._lastSwipeDir = "";
+
+    // We only want to activate history swipe animations if we store snapshots.
+    // If we don't store any, we handle horizontal swipes without animations.
+    if (this._maxSnapshots > 0) {
+      this.active = true;
+      gBrowser.addEventListener("pagehide", this, false);
+      gBrowser.addEventListener("pageshow", this, false);
+      gBrowser.addEventListener("popstate", this, false);
+      gBrowser.tabContainer.addEventListener("TabClose", this, false);
+    }
   },
 
   /**
@@ -581,10 +586,12 @@ let gHistorySwipeAnimation = {
       this._historyIndex = gBrowser.webNavigation.sessionHistory.index;
       this._canGoBack = this.canGoBack();
       this._canGoForward = this.canGoForward();
-      this._takeSnapshot();
-      this._installPrevAndNextSnapshots();
-      this._addBoxes();
-      this._lastSwipeDir = "";
+      if (this.active) {
+        this._takeSnapshot();
+        this._installPrevAndNextSnapshots();
+        this._addBoxes();
+        this._lastSwipeDir = "";
+      }
     }
     this.updateAnimation(0);
   },