There are several options (?_ab=0&_fd=0&_sc=1) included in a theme preview URL. What do each of them do exactly? I also noticed that there's some inheritance when viewing the CSS in Chrome Dev Tools, which includes a pb=0 that isn't included in the preview URL.
https://shopname.myshopify.com/?_ab=0&_fd=0&_sc=1&preview_theme_id=12345678910
