--- a/devtools/bootstrap.js
+++ b/devtools/bootstrap.js
@@ -52,11 +52,14 @@ function shutdown(data, reason) {
   // On browser shutdown, do not try to cleanup anything
   if (reason == APP_SHUTDOWN) {
     return;
   }
 
   unload("disable");
 }
 
-function install() {}
+function install() {
+  const {DevToolsShim} = Cu.import("chrome://devtools-shim/content/DevToolsShim.jsm", {});
+  DevToolsShim.setInstalled(true);
+}
 
 function uninstall() {}

--- a/devtools/shim/DevToolsShim.jsm
+++ b/devtools/shim/DevToolsShim.jsm
@@ -37,16 +37,17 @@ function removeItem(array, callback) {
  * the DevToolsShim will forward all the requests received until then to the real DevTools
  * instance.
  *
  * DevToolsShim.isInstalled() can also be used to know if DevTools are currently
  * installed.
  */
 this.DevToolsShim = {
   _gDevTools: null,
+  _installed: false,
   listeners: [],
   tools: [],
   themes: [],
 
   /**
    * Lazy getter for the `gDevTools` instance. Should only be called when users interacts
    * with DevTools as it will force loading them.
    *
@@ -65,19 +66,21 @@ this.DevToolsShim = {
   },
 
   /**
    * Check if DevTools are currently installed (but not necessarily initialized).
    *
    * @return {Boolean} true if DevTools are installed.
    */
   isInstalled: function () {
-    return Services.io.getProtocolHandler("resource")
-             .QueryInterface(Ci.nsIResProtocolHandler)
-             .hasSubstitution("devtools");
+    return this._installed;
+  },
+
+  setInstalled: function (installed) {
+    this._installed = installed;
   },
 
   /**
    * Check if DevTools have already been initialized.
    *
    * @return {Boolean} true if DevTools are initialized.
    */
   isInitialized: function () {