What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I've cloned your JotForm to check the issue with checkbox. I tried to edit the cloned JotForm with Mozilla Firefox v33 and Safari 6. But, I was not able to see any issue with the widget.
This could be an issue with the browser cache. We request you to try clearing the browser cache by following the steps provided in the guide http://www.wikihow.com/Clear-Your-Browser%27s-Cache
Please let us know if the issue still persists. We will be happy to look into this issue further.