Works in IE, but not Chrome or Firefox

Just made a site for a client – https://www.missionaussies.com – and Contact Form 7 works with Internet Explorer, but not Chrome or Firefox. When I write that it works, I mean when you click “Send” an animation runs alongside the send button and then a message, “Thank you for your message. It has been sent.” appears below the blue send button. When you click the send button in Chrome or Firefox, nothing happens. I wish I was smart enough to understand what the issue was, but I’m hitting a wall at this point. Any help would be massively appreciated.