Tweak exit popup script

I need an exit popup that functions like the exit popup contained in the attached text file, but I need it to only attach to the tab/window closing. I currently have a squeeze page with an optin form. The problem is, if someone submits the optin form, this exit popup is also firing. I need it to only fire if someone closes the tab/window. It mustn't fire if someone leaves the page by filling out the optin form. This script works well in that it redirects to the redirect page at the same time as showing the popup message. I want that functionality to remain. But I only want the script to attach to the tab/window closing, not to someone submitting the form. You may change the jquery version and anything else, as long as the functionalities I mentioned above are met and that it is cross-browser compatible. Please see the attached text file for the script as it currently is and some other notes. Thanks.