Is it safe to navigate away from the page when the screenshots are being generated?

Yes. If you navigate away from the page the processing of the screenshots will continue. When you come back to the page, if the processing is not complete, you will see the processing in progress. However, if processing has completed, you can access the screenshots from the History dropdown in the URL bar. If you are a registered user, you can also use the 'Email me on completion' option to receive an email when the processing has completed.