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Based on the subject it would seem that if you go into the Form Builder while using your Mac your Submit button gets deleted.
Now, I presume that this is not the case (but wanted to make sure), as I presume that the issue is with your form having the submit button not shown when you access your website over the Mac.
If that is true, do try to use the iframe embed code which we will help you in setting up the height (if needed), but this should stop your iframe from resizing to hide the submit button.