diff --git a/README.md b/README.md
index adea4270..17cebb2c 100644
--- a/README.md
+++ b/README.md
@@ -173,6 +173,7 @@ HTML5 / [APIs](https://wiki.mozilla.org/WebAPI) / [DOM](https://en.wikipedia.org
 * When webGL is enabled, disable webGL extensions [ [1](https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API#WebGL_debugging_and_testing) ]
 * When webGL is enabled, force enabling it even when layer acceleration is not supported [ [1](https://trac.torproject.org/projects/tor/ticket/18603) ]
 * When webGL is enabled, do not expose information about the graphics driver [ [1](https://bugzilla.mozilla.org/show_bug.cgi?id=1171228) [2](https://developer.mozilla.org/en-US/docs/Web/API/WEBGL_debug_renderer_info) ]
+* Spoof single-core CPU [ [1](https://trac.torproject.org/projects/tor/ticket/21675) ]
 
 ### Misc
 
diff --git a/user.js b/user.js
index 434ce75e..0688ead1 100644
--- a/user.js
+++ b/user.js
@@ -186,6 +186,10 @@ user_pref("webgl.enable-debug-renderer-info",			false);
 // somewhat related...
 //user_pref("pdfjs.enableWebGL",					false);
 
+// PREF: Spoof single-core CPU
+// https://trac.torproject.org/projects/tor/ticket/21675
+user_pref("dom.maxHardwareConcurrency",				false);
+
 /******************************************************************************
  * SECTION: Misc                                                              *
  ******************************************************************************/