I've seen that a few other people have had this same problem, so I followed the instructions posted, but am still having the same issue. I downloaded Evernote from the web, and installed it that way. I downloaded Evernote Web Clipper from the web (called Evernote.5.9.10.safariextz) I move the installer onto my desktop. Then, I double-click the installer, and it says "Evernote.5.9.10.safariextz is an appliation downloaded from the Internet. Are you sure you want to open it?" I click "Open." Then I get a window that says "Are you sure you want to install the extension “Evernote Web Clipper”?"