How to get content_scripts to execute in file:/// URLs in a Chrome extension

Question

I can't seem to make this work no matter what I do. Let me demonstrate with a very simple example extension. Here is the manifest.json:

{
  "manifest_version": 2,

  "name": "Sample Of Content Script",
  "description": "Changes the background of a page pink",
  "version": "1.0",

  "content_scripts": [
    {
      "matches": [ "<all_urls>" ],
      "js": [ "changer.js" ]
    }
  ],

  "permissions": [
    "webNavigation"
  ],

  "background": {
    "scripts": [ "background.js" ]
  }
}

Notice that my content_scripts entry matches all_urls, which (according to Google documentation) should match file:/// URLs.

The background.js:

(function (chrome) {
    'use strict';

    chrome.webNavigation.onCompleted.addListener(function (details) {
        chrome.tabs.sendMessage(details.tabId, {
            action: 'changeBackground',
            color: 'pink'
        });
    });

})(chrome);

And the changer.js (content script):

(function (chrome) {
    'use strict';

    chrome.runtime.onMessage.addListener(function (request) {
        if (request.action !== 'changeBackground') { return; }
        document.body.style.background = request.color;
    });

})(chrome);

This extension has been published on the Chrome Web Store so you can see the result in action:

https://chrome.google.com/webstore/detail/sample-of-content-script/bkekbfjgkkineeokljnobgcoadlhdckd

It's a pretty simple extension. Navigate to a page, and it turn's the page's background pink. Unfortunately, it doesn't work for any file:/// URLs. The changer.js script is not loaded into the page, and nothing happens.

Extra info

• It actually seems to work just fine when running as an Unpacked extension in Developer mode. Pages loaded from the file system turn pink.
• I tried using chrome.tabs.executeScript() instead of putting the script into the manifest. This failed in a more obvious way, saying that I didn't request permissions to modify file:/// URLs in the manifest.
• I added "file:///*/*" to the permissions section of manifest.json. That seemed to workwell with chrome.tabs.executeScript(), but the Chrome Web Store rejected the extension, saying that file:/// permissions are not allowed.
• I reverted to a content_script section in manifest.json and tried adding "file:///*/* to the matches section in the manifest. Again, this worked in a development build, but when I uploaded it to the Chrome Web Store and then installed it, it didn't work.

Answer 1

<all_urls> indeed covers file:// scheme, but it must be manually activated in the extensions list.

If an extension has permissions that cover file:// scheme, it will have a checkbox "Allow access to file URLs" next to "Allow in incognito". The user must enable that manually; you can help by creating a tab with preconfigured URL, after explaining the process:

chrome.tabs.create({url: "chrome://extensions/?id=" + chrome.runtime.id});