Issue 5953 - Bypass site CSP for script injection in Firefox

inject.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 380 matching lines @@
 if (document instanceof HTMLDocument)
 {
   let sandbox = window.frameElement &&
                 window.frameElement.getAttribute("sandbox");
 
   if (typeof sandbox != "string" || /(^|\s)allow-scripts(\s|$)/i.test(sandbox))
   {
     let script = document.createElement("script");
     script.type = "application/javascript";
     script.async = false;
-    let code = "(" + injected + ")('" + randomEventName + "');";
-    let blob = new Blob([code]);

[Sebastian Noack, 2017/11/03 21:12:15]

Nit: At least this temporary variable can be avoided.

[kzar, 2017/11/06 11:32:51]

Yea, how about this?

let url = URL.createObjectURL(new Blob([
  "(" + injected + ")('" + randomEventName + "');"
]));

Also would you mind adding a comment to explain why we're using this approach to
inject the code?

-    let url = URL.createObjectURL(blob);
+    // Firefox 58 only bypasses site CSPs when assigning to 'src'.
+    let url = URL.createObjectURL(new Blob([
+      "(" + injected + ")('" + randomEventName + "');"
+    ]));
     script.src = url;
     document.documentElement.appendChild(script);
     document.documentElement.removeChild(script);
     URL.revokeObjectURL(url);
   }
 }