1 files changed, 13 insertions, 5 deletions
diff --git a/content_scripts/scroller.coffee b/content_scripts/scroller.coffee
index 3a1b3772..a533c161 100644
--- a/content_scripts/scroller.coffee
+++ b/content_scripts/scroller.coffee
@@ -128,13 +128,15 @@ checkVisibility = (element) ->
 CoreScroller =
   init: ->
     @time = 0
-    @lastEvent = null
-    @keyIsDown = false
+    @lastEvent = @keyIsDown = @cancelEventListenerId = null
 
+  # This installs listeners for events which should cancel smooth scrolling.
+  installCanceEventListener: ->
+    @removeCancelEventListener()
     # NOTE(smblott) With extreme keyboard configurations, Chrome sometimes does not get a keyup event for
     # every keydown, in which case tapping "j" scrolls indefinitely.  This appears to be a Chrome/OS/XOrg bug
     # of some kind.  See #1549.
-    handlerStack.push
+    @cancelEventListenerId = handlerStack.push
       _name: 'scroller/track-key-status'
       keydown: (event) =>
         handlerStack.alwaysContinueBubbling =>
@@ -149,6 +151,10 @@ CoreScroller =
         handlerStack.alwaysContinueBubbling =>
           @time += 1 if event.target == window
 
+  removeCancelEventListener: ->
+    handlerStack.remove @cancelEventListenerId if @cancelEventListenerId?
+    @cancelEventListenerId = @lastEvent = @keyIsDown = null
+
   # Return true if CoreScroller would not initiate a new scroll right now.
   wouldNotInitiateScroll: -> @lastEvent?.repeat and Settings.get "smoothScroll"
 
@@ -175,7 +181,7 @@ CoreScroller =
     return if @lastEvent?.repeat
 
     activationTime = ++@time
-    myKeyIsStillDown = => @time == activationTime and @keyIsDown
+    myKeyIsStillDown = => @time == activationTime and @keyIsDown ? true
 
     # Store amount's sign and make amount positive; the arithmetic is clearer when amount is positive.
     sign = getSign amount
@@ -215,13 +221,15 @@ CoreScroller =
         requestAnimationFrame animate
       else
         # We're done.
+        @removeCancelEventListener()
         checkVisibility element
 
     # If we've been asked not to be continuous, then we advance time, so the myKeyIsStillDown test always
     # fails.
     ++@time unless continuous
 
-    # Launch animator.
+    # Start scrolling.
+    @installCanceEventListener()
     requestAnimationFrame animate
 
 # Scroller contains the two main scroll functions which are used by clients.