How to disable context menu on right click/long touch in a kiosk mode of Chrome?

I assume you're displaying a plain http://... (or possibly https://... or file://...) Web page on your kiosk. If you're actually showing an app (i.e., chrome-extension://...), then this strategy will not work.

A Chrome extension that injects window.addEventListener("contextmenu", function(e) { e.preventDefault(); }) into every browsing context would probably do the trick to block context menus on iframes.

manifest.json:

{
    "manifest_version": 2,
    "name": "Context Menu Blocker",
    "version": "1.0",
    "content_scripts": [
      {
        "matches": ["<all_urls>"],
        "js": ["contextblocker.js"],
        "all_frames": true,
        "match_about_blank": true
      }
    ]
}

contextblocker.js:

window.addEventListener("contextmenu", function(e) { e.preventDefault(); })

Simply create a folder and place the two files inside. Then, go to chrome://extensions/, check the Developer Mode box. Finally, click Load unpacked extension... and select the folder you just created.

This should prevent the context menu from appearing in anywhere extension content scripts are allowed to run, include any page loaded inside of an iframe. There are few notable points where it fails:

• Extensions are not allowed to run on chrome:// or chrome-extension:// pages, or on Google's Web Store. If your kiosk is displaying an app, this whole strategy won't work, because this extension won't be able to access iframes inside of another app or extension (even if the source of the iframe is an origin that it would normally have permission to access).
• If you navigate directly to about:blank, the content script will not run and the context menu can appear. (If about:blank is loaded in an iframe, however, the block will work correctly.)
• If an iframe has a sandbox attribute that does not include the allow-scripts permission, then the extension cannot block context menus from that iframe.

As long as none of those restrictions apply (and as long as a script on the page itself does not clear all event listeners on window), then it should work.

I have used the code above to create a simple extension in the Chrome Web Store. (Developer-mode extensions now produce a warning on start-up, while Web Store extensions do not.)

If you're using jQuery, the below code will disable the context menu (aka 'right click').

$(document).on("contextmenu",function(){
       return false;
    }); 
});