diff --git a/AppKit/CPScrollView.j b/AppKit/CPScrollView.j
index 3ea8593b9..c93543315 100644
--- a/AppKit/CPScrollView.j
+++ b/AppKit/CPScrollView.j
@@ -1403,7 +1403,16 @@ Notifies the delegate when the scroll view has finished scrolling.
     if (![_horizontalScroller isHidden] || ![_verticalScroller isHidden])
         _timerScrollersHide = [CPTimer scheduledTimerWithTimeInterval:CPScrollViewFadeOutTime target:self selector:@selector(_hideScrollers:) userInfo:nil repeats:NO];
 
-    [self _respondToScrollWheelEventWithDeltaX:[anEvent deltaX] deltaY:[anEvent deltaY]];
+    var deltaX = [anEvent scrollingDeltaX],
+        deltaY = [anEvent scrollingDeltaY];
+
+    if (![anEvent hasPreciseScrollingDeltas])
+    {
+        deltaX *= (_horizontalLineScroll || 1.0);
+        deltaY *= (_verticalLineScroll || 1.0);
+    }
+
+    [self _respondToScrollWheelEventWithDeltaX:deltaX deltaY:deltaY];
 }
 
 - (void)scrollPageUp:(id)sender
diff --git a/AppKit/Platform/DOM/CPPlatformWindow+DOM.j b/AppKit/Platform/DOM/CPPlatformWindow+DOM.j
index ad288aae4..b0610b5f2 100644
--- a/AppKit/Platform/DOM/CPPlatformWindow+DOM.j
+++ b/AppKit/Platform/DOM/CPPlatformWindow+DOM.j
@@ -203,7 +203,9 @@ var ModifierKeyCodes = [
 var resizeTimer = nil;
 var PreventScroll = true;
 
-#define FIREFOX_SCROLLWHEEL_FACTOR 6
+// When scrolling with an old-style scroll wheel with discete steps ('clicks'), the scroll amount can indicate how many "lines" to
+// scroll.
+#define SCROLLWHEEL_LINE_PIXELS 6.0
 
 #if PLATFORM(DOM)
 
@@ -919,9 +921,22 @@ var PreventScroll = true;
     // We lag 1 event behind without this timeout.
     setTimeout(function()
     {
-        // Find the scroll delta
-        var deltaX = _DOMScrollingElement.scrollLeft - 150,
-            deltaY = (_DOMScrollingElement.scrollTop - 150) || (aDOMEvent.deltaY === undefined ? 0 : (aDOMEvent.deltaY * FIREFOX_SCROLLWHEEL_FACTOR));
+        if (aDOMEvent.deltaMode !== undefined && aDOMEvent.deltaMode !== 0)
+        {
+            event._hasPreciseScrollingDeltas = NO;
+            event._scrollingDeltaX = aDOMEvent.deltaX;
+            event._scrollingDeltaY = aDOMEvent.deltaY;
+            event._deltaX = aDOMEvent.deltaX * SCROLLWHEEL_LINE_PIXELS;
+            event._deltaY = aDOMEvent.deltaY * SCROLLWHEEL_LINE_PIXELS;
+        }
+        else
+        {
+            event._hasPreciseScrollingDeltas = YES;
+            event._scrollingDeltaX = (_DOMScrollingElement.scrollLeft - 150) || aDOMEvent.deltaX || 0;
+            event._scrollingDeltaY = (_DOMScrollingElement.scrollTop - 150) || aDOMEvent.deltaY || 0;
+            event._deltaX = event._scrollingDeltaX;
+            event._deltaY = event._scrollingDeltaY;
+        }
 
         // If we scroll super with momentum,
         // there are so many events going off that
@@ -932,13 +947,8 @@ var PreventScroll = true;
         //
         // We get free performance boost if we skip sending these events,
         // as sending a scroll event with no deltas doesn't do anything.
-        if (deltaX || deltaY)
-        {
-            event._deltaX = deltaX;
-            event._deltaY = deltaY;
-
+        if (event._deltaX || event._deltaY)
             [CPApp sendEvent:event];
-        }
 
         // We set StopDOMEventPropagation = NO on line 1008
         //if (StopDOMEventPropagation)