populate-popup currently provides no information about why the popup menu is being opened. It should allow the user to distinguish when a selection, a link or other object has been clicked, and give information about that (the link, the selection, etc). It should also allow the user to stop the default handler from running by returning a boolean.
All these problems would be solved by the new contex-menu signal, see bug https://bugs.webkit.org/show_bug.cgi?id=49904
Hi Thadeu! Is this bug still relevant? Hopefully the “context-menu” signal solved the issue for you, as Carlos mentioned. Could you please let us know if that's working for you?