diff --git a/toolkit/devtools/Loader.jsm b/toolkit/devtools/Loader.jsm
index 2b0970a94a3..8161df9d2df 100644
--- a/toolkit/devtools/Loader.jsm
+++ b/toolkit/devtools/Loader.jsm
@@ -120,6 +120,7 @@ SrcdirProvider.prototype = {
     let clientURI = this.fileURI(OS.Path.join(toolkitDir, "client"));
     let prettyFastURI = this.fileURI(OS.Path.join(toolkitDir), "pretty-fast.js");
     let asyncUtilsURI = this.fileURI(OS.Path.join(toolkitDir), "async-utils.js");
+    let contentObserverURI = this.fileURI(OS.Path.join(toolkitDir), "content-observer.js");
     let gcliURI = this.fileURI(OS.Path.join(toolkitDir, "gcli", "source", "lib", "gcli"));
     let acornURI = this.fileURI(OS.Path.join(toolkitDir, "acorn"));
     let acornWalkURI = OS.Path.join(acornURI, "walk.js");
@@ -144,6 +145,7 @@ SrcdirProvider.prototype = {
         "devtools/client": clientURI,
         "devtools/pretty-fast": prettyFastURI,
         "devtools/async-utils": asyncUtilsURI,
+        "devtools/content-observer": contentObserverURI,
         "gcli": gcliURI,
         "acorn": acornURI,
         "acorn/util/walk": acornWalkURI