While popups blocker is good to prevent unwanted popups, it can interfere with legitimate popup functions in application like Square. Follow the steps in the links below to enable popups in your favorite browser
In Firefox, you need to add the domain name Paypal.com to an allowed or exceptions list. Once you add this to the list, you should be able to use the application normally. Click here to learn to manage pop-up blocker settings in Firefox.
Similar to Firefox, you need to add Paypal.com to an allowed list of sites . Click here to learn how to do that
Click here to learn on how to enable popups in Internet Explorer