I've been an Opera user for many, maybe 10 years or more. Now I decided to try Evernote and in Opera 12.16 it is not possible to run a web client of Evernote. Web Evernote window is blank. Even a plugin for Evernote Web Clipper says that it needs at least Opera version 16. So I decided to switch to Firefox.
I exported Opera bookmarks with folders of bookmarks into html format and an import to Firefox was flawless.