I was mostly asking about using Javascript in CEF. I could find the HTML,CSS, and JS to make the menu, but getting that to run on an arbitrary page through CEF is the part that I'm unsure about.
You can inject JavaScript as described at https://bitbucket.org/chromiumembedded/ ... gration.md. However if you don't control the web content there's the possibility of the page interfering. Depending on what options you show in the context menu you might also implement them using your own native code.