Add util.weakReference that won't crash if you pass null.

common/content/dactyl.js

@@ -205,7 +205,7 @@ var Dactyl = Module("dactyl", XPCOM(Ci.nsISupportsWeakReference, ModuleBase), {
     registerObserver: function registerObserver(type, callback, weak) {
         if (!(type in this._observers))
             this._observers[type] = [];
-        this._observers[type].push(weak ? Cu.getWeakReference(callback) : { get: function () callback });
+        this._observers[type].push(weak ? util.weakReference(callback) : { get: function () callback });
     },
 
     registerObservers: function registerObservers(obj, prop) {

common/content/events.js

@@ -50,8 +50,8 @@ var EventHive = Class("EventHive", Contexts.Hive, {
         var [self, events] = this._events(event, callback);
 
         for (let [event, callback] in Iterator(events)) {
-            let args = [Cu.getWeakReference(target),
+            let args = [util.weakReference(target),
-                        self ? Cu.getWeakReference(self) : { get: function () null },
+                        util.weakReference(self),
                         event,
                         this.wrapListener(callback, self),
                         capture,

common/content/marks.js

@@ -65,7 +65,7 @@ var Marks = Module("marks", {
         let mark = this.Mark();
 
         if (Marks.isURLMark(name)) {
-            mark.tab = Cu.getWeakReference(tabs.getTab());
+            mark.tab = util.weakReference(tabs.getTab());
             this._urlMarks.set(name, mark);
             var message = "mark.addURL";
         }

common/content/modes.js

@@ -333,7 +333,7 @@ var Modes = Module("modes", {
         if (!(id in this.boundProperties))
             for (let elem in array.iterValues(this._modeStack))
                 elem.saved[id] = { obj: obj, prop: prop, value: obj[prop], test: test };
-        this.boundProperties[id] = { obj: Cu.getWeakReference(obj), prop: prop, test: test };
+        this.boundProperties[id] = { obj: util.weakReference(obj), prop: prop, test: test };
     },
 
     inSet: false,

common/modules/buffer.jsm

@@ -127,11 +127,12 @@ var Buffer = Module("Buffer", {
      */
     get lastInputField() {
         let field = this.localStore.lastInputField && this.localStore.lastInputField.get();
+
         let doc = field && field.ownerDocument;
         let win = doc && doc.defaultView;
         return win && doc === win.document ? field : null;
     },
-    set lastInputField(value) { this.localStore.lastInputField = value && Cu.getWeakReference(value); },
+    set lastInputField(value) { this.localStore.lastInputField = util.weakReference(value); },
 
     /**
      * @property {nsIURI} The current top-level document.
@@ -241,7 +242,7 @@ var Buffer = Module("Buffer", {
         return frame && frame.get() || this.win;
     },
     set focusedFrame(frame) {
-        this.localStore.focusedFrame = Cu.getWeakReference(frame);
+        this.localStore.focusedFrame = util.weakReference(frame);
     },
 
     /**

common/modules/contexts.jsm

@@ -30,7 +30,7 @@ var Group = Class("Group", {
 
     get contexts() this.modules.contexts,
 
-    set lastDocument(val) { this._lastDocument = val && Cu.getWeakReference(val); },
+    set lastDocument(val) { this._lastDocument = util.weakReference(val); },
     get lastDocument() this._lastDocument && this._lastDocument.get(),
 
     modifiable: true,

common/modules/finder.jsm

@@ -339,10 +339,10 @@ var RangeFinder = Module("rangefinder", {
  */
 var RangeFind = Class("RangeFind", {
     init: function init(window, content, matchCase, backward, elementPath, regexp) {
-        this.window = Cu.getWeakReference(window);
+        this.window = util.weakReference(window);
         this.content = content;
 
-        this.baseDocument = Cu.getWeakReference(this.content.document);
+        this.baseDocument = util.weakReference(this.content.document);
         this.elementPath = elementPath || null;
         this.reverse = Boolean(backward);
 
@@ -381,7 +381,7 @@ var RangeFind = Class("RangeFind", {
         this.range.selectionController.scrollSelectionIntoView(
             this.range.selectionController.SELECTION_NORMAL, 0, false);
 
-        this.store.focusedFrame = Cu.getWeakReference(range.startContainer.ownerDocument.defaultView);
+        this.store.focusedFrame = util.weakReference(range.startContainer.ownerDocument.defaultView);
     },
 
     cancel: function cancel() {

common/modules/overlay.jsm

@@ -74,7 +74,7 @@ var Overlay = Module("Overlay", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReferen
             [self, events] = [event, event[callback || "events"]];
 
         for (let [event, callback] in Iterator(events)) {
-            let args = [Cu.getWeakReference(target),
+            let args = [util.weakReference(target),
                         event,
                         util.wrapCallback(callback, self),
                         capture,

common/modules/prefs.jsm

@@ -113,7 +113,7 @@ var Prefs = Module("prefs", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference])
 
         if (!this._observers[pref])
             this._observers[pref] = [];
-        this._observers[pref].push(!strong ? Cu.getWeakReference(callback) : { get: function () callback });
+        this._observers[pref].push(!strong ? util.weakReference(callback) : { get: function () callback });
     },
 
     /**

common/modules/storage.jsm

@@ -214,7 +214,7 @@ var Storage = Module("Storage", {
         if (ref) {
             let refs = overlay.getData(ref, "storage-refs");
             refs.push(callback);
-            var callbackRef = Cu.getWeakReference(callback);
+            var callbackRef = util.weakReference(callback);
         }
         else {
             callbackRef = { get: function () callback };

common/modules/styles.jsm

@@ -96,7 +96,7 @@ var Hive = Class("Hive", {
     get modifiable() this.name !== "system",
 
     addRef: function (obj) {
-        this.refs.push(Cu.getWeakReference(obj));
+        this.refs.push(util.weakReference(obj));
         this.dropRef(null);
     },
     dropRef: function (obj) {

common/modules/util.jsm

@@ -1550,6 +1550,15 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
         return res.filter(function (h) !Set.add(seen, h.spec));
     },
 
+    /**
+     * Like Cu.getWeakReference, but won't crash if you pass null.
+     */
+    weakReference: function weakReference(jsval) {
+        if (jsval == null)
+            return { get: function get() null };
+        return Cu.getWeakReference(jsval);
+    },
+
     /**
      * Wraps native exceptions thrown by the called function so that a
      * proper stack trace may be retrieved from them.