Same Origin Policy is an important security concept for some client-side programming languages, such as JavaScript. The policy allows scripts located on the pages of one site to access each other's methods and properties without restrictions, but prevents access to most methods and properties for pages on different sites. Identical sources are sources for which three characteristics coincide:

1. Domain
2. Port
3. Protocol

Thus, when using widgets built into your site, you will not be able to access them using JavaScript, just as the code from iframe itself will not be able to affect your site. You will be protected from scripts of third-party sites, but also limited in the possibilities of influencing the widget. For example: when switching form pages, using page breaks, your page will not scroll to top.

You can read more about Same Origin Policy on browser support sites:

Firefox