From 0671510313cd983dde9ac23f589bac1607fcf347 Mon Sep 17 00:00:00 2001
From: Stephen Pohl <spohl.mozilla.bugs@gmail.com>
Date: Tue, 29 Oct 2013 15:03:05 -0400
Subject: [PATCH] Bug 931787: Avoid tracking vertical overscrolls on OSX if
 elastic overscroll is disabled. r=felipe

---
 .../base/content/browser-gestureSupport.js    | 29 +++++++++++--------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/browser/base/content/browser-gestureSupport.js b/browser/base/content/browser-gestureSupport.js
index 9c8d4c5b4d9..50ede96fe63 100644
--- a/browser/base/content/browser-gestureSupport.js
+++ b/browser/base/content/browser-gestureSupport.js
@@ -176,7 +176,8 @@ let gGestureSupport = {
   },
 
   /**
-   * Sets up the history swipe animations for a swipe gesture event, if enabled.
+   * Sets up swipe gestures. This includes setting up swipe animations for the
+   * gesture, if enabled.
    *
    * @param aEvent
    *        The swipe gesture start event.
@@ -189,18 +190,22 @@ let gGestureSupport = {
     }
 
     let isVerticalSwipe = false;
-    if (gHistorySwipeAnimation.active) {
-      if (aEvent.direction == aEvent.DIRECTION_UP) {
-        if (content.pageYOffset > 0) {
-          return false;
-        }
-        isVerticalSwipe = true;
-      } else if (aEvent.direction == aEvent.DIRECTION_DOWN) {
-        if (content.pageYOffset < content.scrollMaxY) {
-          return false;
-        }
-        isVerticalSwipe = true;
+    if (aEvent.direction == aEvent.DIRECTION_UP) {
+      if (content.pageYOffset > 0) {
+        return false;
       }
+      isVerticalSwipe = true;
+    } else if (aEvent.direction == aEvent.DIRECTION_DOWN) {
+      if (content.pageYOffset < content.scrollMaxY) {
+        return false;
+      }
+      isVerticalSwipe = true;
+    }
+    if (isVerticalSwipe && !gHistorySwipeAnimation.active) {
+      // Unlike horizontal swipes (which can navigate history even when
+      // swipe animations are turned off) vertical swipes should not be tracked
+      // if animations (bounce effect) aren't enabled.
+      return false;
     }
 
     let canGoBack = gHistorySwipeAnimation.canGoBack();