Fans of little tech savvy browser will be happy to know that, Opera now supports and uses the official java plugin (latest nightly builds that is), rather then the horrible custom plugin they’ve been using for years.
This means java applets should now work as expected across all browsers and Opera 
LWJGL applets now work flawlessly.
JavaFX applets technically should work too but looks like the javascript code on javafx.com specifically blocks/excludes Opera, so they don’t work yet.