What are some alternatives?
Hover Zoom - Enlarge thumbnails on mouse over.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
ezLinkPreview - Browse more efficiently: Preview links and images without leaving your current tab.
Tutanota - Get your encrypted mailbox for free.
Thumbnail Zoom Plus - The official site of the Thumbnail Zoom Plus add-on for Firefox
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.