Why does a security error occur when using getUrl() in Firefox WebExtension?

Question

Mozilla Firefox

I'm trying to port an extension from Chrome and I get this error:
Security Error: Content at " example.com " may not load or link to "moz-extension://04d69802-c26f-47ae-86f2-d54650455e5a/blocks/indicators/__icon/indicators__icon -tweet.png"

(function () {
  'use strict';
  var PATHS = {
    TWITTER: chrome.extension.getURL("blocks/indicators/__icon/indicators__icon-tweet.png")
  };
})();

In manifest.json , the paths are specified in web_accessible_resources .