Opera has decent digital certificate support, with the second best initial cipher offering (behind Firefox), but there's one notable exception. Although the first five ciphers use 256-bit AES keys, strangely Opera does not yet support ECC (Elliptical Curve Cryptography), which is the strongest asymmetric cipher standard in use today. OCSP (Online Certificate Status Protocol) is supported by default, and the minimum SSL version can be specified.
Opera lets you view installed and registered plug-ins, but not manage them. However, a neat little feature that the other browsers don't have is the ability to specify which requests for plug-ins Opera should ignore. Most browsers bug the user repeatedly each time a reloaded Web page requires a specific control; only Opera and IE 8 allow per-site control. On an interesting note, Opera has integrated BitTorrent support, which some security administrators may not like.
Opera has another feature that allows site-specific CSS (called author mode) to be replaced by a user-specific CSS (known as user mode). Both author and user mode can be customized, allowing you to determine exactly what is supported in each mode. A similar option was added to Internet Explorer 8 and is part of the CSS 2.1 standard called Alternative Style Sheets.
Opera has another nice feature, kiosk mode, that is designed to be run on public information computers. Kiosk mode disables tool bars, requires full-screen window sizes, disables many paths to system areas, and can be used to prevent downloads. After a period of inactivity, it will return to the defined home page.