For some reason, Safari (and the other browsers, which are Safari in disguise) doesn't let us block the context menu on iOS. If you right-click there, the event is passed through to the session, but also pops up a local menu. This menu is in the way and just generally annoying.
Right click on iOS is probably rare, though, as you need to hook up a trackpad or mouse to it. The iPad Pro has a trackpad in its fancy cover, though.
To right-click, you either press Ctrl+click (which means you need a physical keyboard as well), or you do a two-finger click. The latter only works on newer trackpads, though.
Originally reported upstream: