I'm at work, trying to pay our internet service provider. They want us to use their Portal to submit payment, which I would have no problem doing if my browser worked with their site. I have both Mozilla Firefox and Opera; unfortunately the only browser the site works with is Internet Explorer.
My advice: Never make it difficult for the client to pay you. Even if the other features on the site will not work with the client's browser, at least make the payment part functional.