--- a/toolkit/content/browser-content.js
+++ b/toolkit/content/browser-content.js
@@ -129,20 +129,36 @@ var ClickEventHandler = {
 
   startScroll(event) {
 
     this.findNearestScrollableElement(event.originalTarget);
 
     if (!this._scrollable)
       return;
 
+    let domUtils = content.QueryInterface(Ci.nsIInterfaceRequestor)
+                          .getInterface(Ci.nsIDOMWindowUtils);
+    let scrollable = this._scrollable;
+    if (scrollable instanceof Ci.nsIDOMWindow) {
+      // getViewId() needs an element to operate on.
+      scrollable = scrollable.document.documentElement;
+    }
+    let scrollId = null;
+    try {
+      scrollId = domUtils.getViewId(scrollable);
+    } catch (e) {
+      // No view ID - leave it as null. Receiving side will check.
+    }
+    let presShellId = domUtils.getPresShellId();
     let [enabled] = sendSyncMessage("Autoscroll:Start",
                                     {scrolldir: this._scrolldir,
                                      screenX: event.screenX,
-                                     screenY: event.screenY});
+                                     screenY: event.screenY,
+                                     scrollId,
+                                     presShellId});
     if (!enabled) {
       this._scrollable = null;
       return;
     }
 
     Services.els.addSystemEventListener(global, "mousemove", this, true);
     addEventListener("pagehide", this, true);