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Unfortunately, you can't add a script in a form. They will simply get stripped out if you add one. But would you mind letting us know what script is that? Like box? IF you're trying to add a Facebook like box, that is possible by using our widget:
We also have some other Facebook and social widgets:
Here's how to add a widget in your form: http://www.jotform.com/help/252-How-to-Add-a-Widget-to-your-Form.
It's the the conversion pixel of Facebook.
Also, I would try to insert conversion tracker from Google AdWords.
I believe to achieve your requirement you will have to create your own custom page and add the "Conversion Pixel" code within the <head> tag of your page. You can then use this page in our custom thank you URL. The following guide should help you: http://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page
It is not possible to add the script to the form itself.