When opening a form and saving the record, then clicking the reference pop-up icon to view a related record, and then clicking the browser back button to return to the original form, the navigation is redirected to the referenced record instead of the original form.

This is expected behaviour. Using the browser's back button confuses the navigation stack. This is why the form's green back button is provided.

Do not use the browser back button when returning from viewing related records. Use the ServiceNow provided green back button in the record header.