I am developing an application that process the PDF form and then echo's confirmation via HTML once the form data is successfully saved in DB. However, if I have firefox open I get following error on PDF form: "An error occurred during submit process. Cannot process content of type text/html. " When I click "ok" I am will not receive confirmation via HTML but the data is stored in DB. In contrast, if the Firefox is closed I get confirmation via default browser (including Firefox) .