I am having the same problem confirm.php hangs. The order form is appearing in my inbox and also the Paypal Sandbox section under test emails is showing that the info is getting to Paypal sandbox as its registering the pretend sale and adding the amount to the account. Something is going wrong with how the page is processing the data that Paypal sandbox sends back.
Don't know if this helps but if I close the browser window on my mac it doesnt do anything as any attempt to open the web page/site still just hangs after pressing submit order. I need to close the application and not just the page then reopen the application to browse the site again after it hangs. This is the same on Firefox, Chrome and Safari.