diff --git a/mozilla/browser/components/preferences/permissions.js b/mozilla/browser/components/preferences/permissions.js
index 40bec3517c5..4a2233b833e 100644
--- a/mozilla/browser/components/preferences/permissions.js
+++ b/mozilla/browser/components/preferences/permissions.js
@@ -170,6 +170,11 @@ var gPermissionManager = {
   
   init: function (aParams)
   {
+    if (this._type) {
+      // reusing an open dialog, clear the old observer
+      this.uninit();
+    }
+
     this._type = aParams.permissionType;
     
     var permissionsText = document.getElementById("permissionsText");