--- a/toolkit/mozapps/extensions/addonManager.js
+++ b/toolkit/mozapps/extensions/addonManager.js
@@ -68,17 +68,17 @@ amManager.prototype = {
   observe: function(aSubject, aTopic, aData) {
     switch (aTopic) {
       case "addons-startup":
         AddonManagerPrivate.startup();
         break;
 
       case "message-manager-close":
       case "message-manager-disconnect":
-        AddonManager.webAPI.clearInstallsFrom(aSubject);
+        this.childClosed(aSubject);
         break;
     }
   },
 
   /**
    * @see amIAddonManager.idl
    */
   mapURIToAddonID: function(uri, id) {
@@ -159,17 +159,47 @@ amManager.prototype = {
 
     return retval;
   },
 
   notify: function(aTimer) {
     AddonManagerPrivate.backgroundUpdateTimerHandler();
   },
 
-  addonListener: null,
+  // Maps message manager instances for content processes to the associated
+  // AddonListener instances.
+  addonListeners: new Map(),
+
+  _addAddonListener(target) {
+    if (!this.addonListeners.has(target)) {
+      let handler = (event, id, needsRestart) => {
+        target.sendAsyncMessage(MSG_ADDON_EVENT, {event, id, needsRestart});
+      };
+      let listener = {
+        onEnabling: (addon, needsRestart) => handler("onEnabling", addon.id, needsRestart),
+        onEnabled: (addon) => handler("onEnabled", addon.id, false),
+        onDisabling: (addon, needsRestart) => handler("onDisabling", addon.id, needsRestart),
+        onDisabled: (addon) => handler("onDisabled", addon.id, false),
+        onInstalling: (addon, needsRestart) => handler("onInstalling", addon.id, needsRestart),
+        onInstalled: (addon) => handler("onInstalled", addon.id, false),
+        onUninstalling: (addon, needsRestart) => handler("onUninstalling", addon.id, needsRestart),
+        onUninstalled: (addon) => handler("onUninstalled", addon.id, false),
+        onOperationCancelled: (addon) => handler("onOperationCancelled", addon.id, false),
+      };
+      this.addonListeners.set(target, listener);
+      AddonManager.addAddonListener(listener);
+    }
+  },
+
+  _removeAddonListener(target) {
+    if (this.addonListeners.has(target)) {
+      AddonManager.removeAddonListener(this.addonListeners.get(target));
+      this.addonListeners.delete(target);
+    }
+  },
 
   /**
    * messageManager callback function.
    *
    * Listens to requests from child processes for InstallTrigger
    * activity, and sends back callbacks.
    */
   receiveMessage: function(aMessage) {
@@ -223,45 +253,32 @@ amManager.prototype = {
       }
 
       case MSG_INSTALL_CLEANUP: {
         AddonManager.webAPI.clearInstalls(payload.ids);
         break;
       }
 
       case MSG_ADDON_EVENT_REQ: {
+        let target = aMessage.target;
         if (payload.enabled) {
-          if (!this.addonListener) {
-            let target = aMessage.target;
-            let handler = (event, id, needsRestart) => {
-              target.sendAsyncMessage(MSG_ADDON_EVENT, {event, id, needsRestart});
-            };
-            this.addonListener = {
-              onEnabling: (addon, needsRestart) => handler("onEnabling", addon.id, needsRestart),
-              onEnabled: (addon) => handler("onEnabled", addon.id, false),
-              onDisabling: (addon, needsRestart) => handler("onDisabling", addon.id, needsRestart),
-              onDisabled: (addon) => handler("onDisabled", addon.id, false),
-              onInstalling: (addon, needsRestart) => handler("onInstalling", addon.id, needsRestart),
-              onInstalled: (addon) => handler("onInstalled", addon.id, false),
-              onUninstalling: (addon, needsRestart) => handler("onUninstalling", addon.id, needsRestart),
-              onUninstalled: (addon) => handler("onUninstalled", addon.id, false),
-              onOperationCancelled: (addon) => handler("onOperationCancelled", addon.id, false),
-            };
-          }
-          AddonManager.addAddonListener(this.addonListener);
+          this._addAddonListener(target);
         } else {
-          if (this.addonListener) {
-            AddonManager.removeAddonListener(this.addonListener);
-          }
+          this._removeAddonListener(target);
         }
       }
     }
     return undefined;
   },
 
+  childClosed(target) {
+    AddonManager.webAPI.clearInstallsFrom(target);
+    this._removeAddonListener(target);
+  },
+
   sendEvent(target, data) {
     target.sendAsyncMessage(MSG_INSTALL_EVENT, data);
   },
 
   classID: Components.ID("{4399533d-08d1-458c-a87a-235f74451cfa}"),
   _xpcom_factory: {
     createInstance: function(aOuter, aIid) {
       if (aOuter != null)