We have customized firefox 5.0.1 and distributed the locked down version to all our clients(approximately 75,000 globaly) for running our web based application. The locked down details are as below - 1. From the Tool menu - Options - Content tab, we have unchecked 'Block pop-up windows' 2. We have used CSS to hide the menu bar, toolbar, address bar so that the users are not left with the option of changing the URL or any other firefox settings. The users are now complaining that inspite of the pop up blocker being unchecked, their pop ups are getting blocked and they are getting the option bar in the top to allow or disallow pop ups in the future. Note: This is happenning sporadically. Cannot be recreated every time and at will. Any help would be much appreciated. Thanks in advance.