Process a custom form

Hello! I have a custom form built in html. I cannot use my sales force or gravity plugin since the options for the questions are images. How do I collect the data? I would prefer just to use a mailto command, but it only works in chrome. Firefox doesn’t email anything, and Outlook will open the email, but strips out the answers. Is there a simple way to get the answers to 20 questions emailed when the person hits submit? This is the form:
https://www.sigmetrix.com/gdt-questionnaire/