diff --git a/toolkit/devtools/Loader.jsm b/toolkit/devtools/Loader.jsm
index 464705e9aaa0..7c17f98a7bf8 100644
--- a/toolkit/devtools/Loader.jsm
+++ b/toolkit/devtools/Loader.jsm
@@ -68,8 +68,8 @@ BuiltinProvider.prototype = {
         "devtools/client": "resource://gre/modules/devtools/client",
         "devtools/pretty-fast": "resource://gre/modules/devtools/pretty-fast.js",
 
-        "acorn": "resource://gre/modules/devtools/acorn.js",
-        "acorn_loose": "resource://gre/modules/devtools/acorn_loose.js",
+        "acorn": "resource://gre/modules/devtools/acorn",
+        "acorn/util/walk": "resource://gre/modules/devtools/acorn/walk.js",
 
         // Allow access to xpcshell test items from the loader.
         "xpcshell-test": "resource://test"
@@ -115,7 +115,7 @@ SrcdirProvider.prototype = {
     let clientURI = this.fileURI(OS.Path.join(toolkitDir, "client"));
     let prettyFastURI = this.fileURI(OS.Path.join(toolkitDir), "pretty-fast.js");
     let acornURI = this.fileURI(OS.Path.join(toolkitDir, "acorn"));
-    let acornLoosseURI = this.fileURI(OS.Path.join(toolkitDir, "acorn_loose.js"));
+    let acornWalkURI = OS.Path.join(acornURI, "walk.js");
     this.loader = new loader.Loader({
       modules: {
         "toolkit/loader": loader,
@@ -136,7 +136,7 @@ SrcdirProvider.prototype = {
         "devtools/pretty-fast": prettyFastURI,
 
         "acorn": acornURI,
-        "acorn_loose": acornLoosseURI
+        "acorn/util/walk": acornWalkURI
       },
       globals: loaderGlobals,
       invisibleToDebugger: this.invisibleToDebugger
diff --git a/toolkit/devtools/acorn/UPGRADING.md b/toolkit/devtools/acorn/UPGRADING.md
index 52ec0699fd90..45cf02fc7c9a 100644
--- a/toolkit/devtools/acorn/UPGRADING.md
+++ b/toolkit/devtools/acorn/UPGRADING.md
@@ -22,3 +22,7 @@ to:
 4. Copy acorn_loose.js to our tree:
 
        $ cp acorn_loose.js /path/to/mozilla-central/toolkit/devtools/acorn/acorn_loose.js
+
+5. Copy util/walk.js to our tree:
+
+       $ cp util/walk.js /path/to/mozilla-central/toolkit/devtools/acorn/walk.js
diff --git a/toolkit/devtools/acorn/moz.build b/toolkit/devtools/acorn/moz.build
index 8f3524f7d230..079482b9d1fa 100644
--- a/toolkit/devtools/acorn/moz.build
+++ b/toolkit/devtools/acorn/moz.build
@@ -6,9 +6,10 @@
 
 XPCSHELL_TESTS_MANIFESTS += ['tests/unit/xpcshell.ini']
 
-JS_MODULES_PATH = 'modules/devtools'
+JS_MODULES_PATH = 'modules/devtools/acorn'
 
 EXTRA_JS_MODULES += [
     'acorn.js',
     'acorn_loose.js',
+    'walk.js',
 ]
diff --git a/toolkit/devtools/acorn/tests/unit/test_import_acorn.js b/toolkit/devtools/acorn/tests/unit/test_import_acorn.js
index 969893f36c2d..49b2b50cb903 100644
--- a/toolkit/devtools/acorn/tests/unit/test_import_acorn.js
+++ b/toolkit/devtools/acorn/tests/unit/test_import_acorn.js
@@ -6,10 +6,13 @@
  */
 
 function run_test() {
-  const acorn = require("acorn");
-  const acorn_loose = require("acorn_loose");
+  const acorn = require("acorn/acorn");
+  const acorn_loose = require("acorn/acorn_loose");
+  const walk = require("acorn/util/walk");
   do_check_true(isObject(acorn));
   do_check_true(isObject(acorn_loose));
+  do_check_true(isObject(walk));
   do_check_eq(typeof acorn.parse, "function");
   do_check_eq(typeof acorn_loose.parse_dammit, "function");
+  do_check_eq(typeof walk.simple, "function");
 }
diff --git a/toolkit/devtools/acorn/tests/unit/test_lenient_parser.js b/toolkit/devtools/acorn/tests/unit/test_lenient_parser.js
index e72aac0f5c33..794918b6357e 100644
--- a/toolkit/devtools/acorn/tests/unit/test_lenient_parser.js
+++ b/toolkit/devtools/acorn/tests/unit/test_lenient_parser.js
@@ -5,7 +5,7 @@
  * Test that acorn's lenient parser gives something usable.
  */
 
-const acorn_loose = require("acorn_loose");
+const acorn_loose = require("acorn/acorn_loose");
 
 function run_test() {
   let actualAST = acorn_loose.parse_dammit("let x = 10");
diff --git a/toolkit/devtools/acorn/tests/unit/test_same_ast.js b/toolkit/devtools/acorn/tests/unit/test_same_ast.js
index d01916d7abbc..ce2de6076d77 100644
--- a/toolkit/devtools/acorn/tests/unit/test_same_ast.js
+++ b/toolkit/devtools/acorn/tests/unit/test_same_ast.js
@@ -5,7 +5,7 @@
  * Test that Reflect and acorn create the same AST for ES5.
  */
 
-const acorn = require("acorn");
+const acorn = require("acorn/acorn");
 Cu.import("resource://gre/modules/reflect.jsm");
 
 const testCode = "" + function main () {
diff --git a/toolkit/devtools/acorn/walk.js b/toolkit/devtools/acorn/walk.js
new file mode 100644
index 000000000000..4c0d9a7f88d6
--- /dev/null
+++ b/toolkit/devtools/acorn/walk.js
@@ -0,0 +1,313 @@
+// AST walker module for Mozilla Parser API compatible trees
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") return mod(exports); // CommonJS
+  if (typeof define == "function" && define.amd) return define(["exports"], mod); // AMD
+  mod((this.acorn || (this.acorn = {})).walk = {}); // Plain browser env
+})(function(exports) {
+  "use strict";
+
+  // A simple walk is one where you simply specify callbacks to be
+  // called on specific nodes. The last two arguments are optional. A
+  // simple use would be
+  //
+  //     walk.simple(myTree, {
+  //         Expression: function(node) { ... }
+  //     });
+  //
+  // to do something with all expressions. All Parser API node types
+  // can be used to identify node types, as well as Expression,
+  // Statement, and ScopeBody, which denote categories of nodes.
+  //
+  // The base argument can be used to pass a custom (recursive)
+  // walker, and state can be used to give this walked an initial
+  // state.
+  exports.simple = function(node, visitors, base, state) {
+    if (!base) base = exports.base;
+    function c(node, st, override) {
+      var type = override || node.type, found = visitors[type];
+      base[type](node, st, c);
+      if (found) found(node, st);
+    }
+    c(node, state);
+  };
+
+  // A recursive walk is one where your functions override the default
+  // walkers. They can modify and replace the state parameter that's
+  // threaded through the walk, and can opt how and whether to walk
+  // their child nodes (by calling their third argument on these
+  // nodes).
+  exports.recursive = function(node, state, funcs, base) {
+    var visitor = funcs ? exports.make(funcs, base) : base;
+    function c(node, st, override) {
+      visitor[override || node.type](node, st, c);
+    }
+    c(node, state);
+  };
+
+  function makeTest(test) {
+    if (typeof test == "string")
+      return function(type) { return type == test; };
+    else if (!test)
+      return function() { return true; };
+    else
+      return test;
+  }
+
+  function Found(node, state) { this.node = node; this.state = state; }
+
+  // Find a node with a given start, end, and type (all are optional,
+  // null can be used as wildcard). Returns a {node, state} object, or
+  // undefined when it doesn't find a matching node.
+  exports.findNodeAt = function(node, start, end, test, base, state) {
+    test = makeTest(test);
+    try {
+      if (!base) base = exports.base;
+      var c = function(node, st, override) {
+        var type = override || node.type;
+        if ((start == null || node.start <= start) &&
+            (end == null || node.end >= end))
+          base[type](node, st, c);
+        if (test(type, node) &&
+            (start == null || node.start == start) &&
+            (end == null || node.end == end))
+          throw new Found(node, st);
+      };
+      c(node, state);
+    } catch (e) {
+      if (e instanceof Found) return e;
+      throw e;
+    }
+  };
+
+  // Find the innermost node of a given type that contains the given
+  // position. Interface similar to findNodeAt.
+  exports.findNodeAround = function(node, pos, test, base, state) {
+    test = makeTest(test);
+    try {
+      if (!base) base = exports.base;
+      var c = function(node, st, override) {
+        var type = override || node.type;
+        if (node.start > pos || node.end < pos) return;
+        base[type](node, st, c);
+        if (test(type, node)) throw new Found(node, st);
+      };
+      c(node, state);
+    } catch (e) {
+      if (e instanceof Found) return e;
+      throw e;
+    }
+  };
+
+  // Find the outermost matching node after a given position.
+  exports.findNodeAfter = function(node, pos, test, base, state) {
+    test = makeTest(test);
+    try {
+      if (!base) base = exports.base;
+      var c = function(node, st, override) {
+        if (node.end < pos) return;
+        var type = override || node.type;
+        if (node.start >= pos && test(type, node)) throw new Found(node, st);
+        base[type](node, st, c);
+      };
+      c(node, state);
+    } catch (e) {
+      if (e instanceof Found) return e;
+      throw e;
+    }
+  };
+
+  // Find the outermost matching node before a given position.
+  exports.findNodeBefore = function(node, pos, test, base, state) {
+    test = makeTest(test);
+    if (!base) base = exports.base;
+    var max;
+    var c = function(node, st, override) {
+      if (node.start > pos) return;
+      var type = override || node.type;
+      if (node.end <= pos && (!max || max.node.end < node.end) && test(type, node))
+        max = new Found(node, st);
+      base[type](node, st, c);
+    };
+    c(node, state);
+    return max;
+  };
+
+  // Used to create a custom walker. Will fill in all missing node
+  // type properties with the defaults.
+  exports.make = function(funcs, base) {
+    if (!base) base = exports.base;
+    var visitor = {};
+    for (var type in base) visitor[type] = base[type];
+    for (var type in funcs) visitor[type] = funcs[type];
+    return visitor;
+  };
+
+  function skipThrough(node, st, c) { c(node, st); }
+  function ignore(_node, _st, _c) {}
+
+  // Node walkers.
+
+  var base = exports.base = {};
+  base.Program = base.BlockStatement = function(node, st, c) {
+    for (var i = 0; i < node.body.length; ++i)
+      c(node.body[i], st, "Statement");
+  };
+  base.Statement = skipThrough;
+  base.EmptyStatement = ignore;
+  base.ExpressionStatement = function(node, st, c) {
+    c(node.expression, st, "Expression");
+  };
+  base.IfStatement = function(node, st, c) {
+    c(node.test, st, "Expression");
+    c(node.consequent, st, "Statement");
+    if (node.alternate) c(node.alternate, st, "Statement");
+  };
+  base.LabeledStatement = function(node, st, c) {
+    c(node.body, st, "Statement");
+  };
+  base.BreakStatement = base.ContinueStatement = ignore;
+  base.WithStatement = function(node, st, c) {
+    c(node.object, st, "Expression");
+    c(node.body, st, "Statement");
+  };
+  base.SwitchStatement = function(node, st, c) {
+    c(node.discriminant, st, "Expression");
+    for (var i = 0; i < node.cases.length; ++i) {
+      var cs = node.cases[i];
+      if (cs.test) c(cs.test, st, "Expression");
+      for (var j = 0; j < cs.consequent.length; ++j)
+        c(cs.consequent[j], st, "Statement");
+    }
+  };
+  base.ReturnStatement = function(node, st, c) {
+    if (node.argument) c(node.argument, st, "Expression");
+  };
+  base.ThrowStatement = function(node, st, c) {
+    c(node.argument, st, "Expression");
+  };
+  base.TryStatement = function(node, st, c) {
+    c(node.block, st, "Statement");
+    if (node.handler) c(node.handler.body, st, "ScopeBody");
+    if (node.finalizer) c(node.finalizer, st, "Statement");
+  };
+  base.WhileStatement = function(node, st, c) {
+    c(node.test, st, "Expression");
+    c(node.body, st, "Statement");
+  };
+  base.DoWhileStatement = base.WhileStatement;
+  base.ForStatement = function(node, st, c) {
+    if (node.init) c(node.init, st, "ForInit");
+    if (node.test) c(node.test, st, "Expression");
+    if (node.update) c(node.update, st, "Expression");
+    c(node.body, st, "Statement");
+  };
+  base.ForInStatement = function(node, st, c) {
+    c(node.left, st, "ForInit");
+    c(node.right, st, "Expression");
+    c(node.body, st, "Statement");
+  };
+  base.ForInit = function(node, st, c) {
+    if (node.type == "VariableDeclaration") c(node, st);
+    else c(node, st, "Expression");
+  };
+  base.DebuggerStatement = ignore;
+
+  base.FunctionDeclaration = function(node, st, c) {
+    c(node, st, "Function");
+  };
+  base.VariableDeclaration = function(node, st, c) {
+    for (var i = 0; i < node.declarations.length; ++i) {
+      var decl = node.declarations[i];
+      if (decl.init) c(decl.init, st, "Expression");
+    }
+  };
+
+  base.Function = function(node, st, c) {
+    c(node.body, st, "ScopeBody");
+  };
+  base.ScopeBody = function(node, st, c) {
+    c(node, st, "Statement");
+  };
+
+  base.Expression = skipThrough;
+  base.ThisExpression = ignore;
+  base.ArrayExpression = function(node, st, c) {
+    for (var i = 0; i < node.elements.length; ++i) {
+      var elt = node.elements[i];
+      if (elt) c(elt, st, "Expression");
+    }
+  };
+  base.ObjectExpression = function(node, st, c) {
+    for (var i = 0; i < node.properties.length; ++i)
+      c(node.properties[i].value, st, "Expression");
+  };
+  base.FunctionExpression = base.FunctionDeclaration;
+  base.SequenceExpression = function(node, st, c) {
+    for (var i = 0; i < node.expressions.length; ++i)
+      c(node.expressions[i], st, "Expression");
+  };
+  base.UnaryExpression = base.UpdateExpression = function(node, st, c) {
+    c(node.argument, st, "Expression");
+  };
+  base.BinaryExpression = base.AssignmentExpression = base.LogicalExpression = function(node, st, c) {
+    c(node.left, st, "Expression");
+    c(node.right, st, "Expression");
+  };
+  base.ConditionalExpression = function(node, st, c) {
+    c(node.test, st, "Expression");
+    c(node.consequent, st, "Expression");
+    c(node.alternate, st, "Expression");
+  };
+  base.NewExpression = base.CallExpression = function(node, st, c) {
+    c(node.callee, st, "Expression");
+    if (node.arguments) for (var i = 0; i < node.arguments.length; ++i)
+      c(node.arguments[i], st, "Expression");
+  };
+  base.MemberExpression = function(node, st, c) {
+    c(node.object, st, "Expression");
+    if (node.computed) c(node.property, st, "Expression");
+  };
+  base.Identifier = base.Literal = ignore;
+
+  // A custom walker that keeps track of the scope chain and the
+  // variables defined in it.
+  function makeScope(prev, isCatch) {
+    return {vars: Object.create(null), prev: prev, isCatch: isCatch};
+  }
+  function normalScope(scope) {
+    while (scope.isCatch) scope = scope.prev;
+    return scope;
+  }
+  exports.scopeVisitor = exports.make({
+    Function: function(node, scope, c) {
+      var inner = makeScope(scope);
+      for (var i = 0; i < node.params.length; ++i)
+        inner.vars[node.params[i].name] = {type: "argument", node: node.params[i]};
+      if (node.id) {
+        var decl = node.type == "FunctionDeclaration";
+        (decl ? normalScope(scope) : inner).vars[node.id.name] =
+          {type: decl ? "function" : "function name", node: node.id};
+      }
+      c(node.body, inner, "ScopeBody");
+    },
+    TryStatement: function(node, scope, c) {
+      c(node.block, scope, "Statement");
+      if (node.handler) {
+        var inner = makeScope(scope, true);
+        inner.vars[node.handler.param.name] = {type: "catch clause", node: node.handler.param};
+        c(node.handler.body, inner, "ScopeBody");
+      }
+      if (node.finalizer) c(node.finalizer, scope, "Statement");
+    },
+    VariableDeclaration: function(node, scope, c) {
+      var target = normalScope(scope);
+      for (var i = 0; i < node.declarations.length; ++i) {
+        var decl = node.declarations[i];
+        target.vars[decl.id.name] = {type: "var", node: decl.id};
+        if (decl.init) c(decl.init, scope, "Expression");
+      }
+    }
+  });
+
+});
diff --git a/toolkit/devtools/pretty-fast/pretty-fast.js b/toolkit/devtools/pretty-fast/pretty-fast.js
index 1a0645efc593..6ada7fad8248 100644
--- a/toolkit/devtools/pretty-fast/pretty-fast.js
+++ b/toolkit/devtools/pretty-fast/pretty-fast.js
@@ -14,7 +14,7 @@
 }(this, function () {
   "use strict";
 
-  var acorn = this.acorn || require("acorn");
+  var acorn = this.acorn || require("acorn/acorn");
   var sourceMap = this.sourceMap || require("source-map");
   var SourceNode = sourceMap.SourceNode;
 
diff --git a/toolkit/devtools/pretty-fast/tests/unit/head_pretty-fast.js b/toolkit/devtools/pretty-fast/tests/unit/head_pretty-fast.js
index 0dfdca9c59e3..9ad0bbea6edf 100644
--- a/toolkit/devtools/pretty-fast/tests/unit/head_pretty-fast.js
+++ b/toolkit/devtools/pretty-fast/tests/unit/head_pretty-fast.js
@@ -8,7 +8,7 @@ const { devtools } = Cu.import("resource://gre/modules/devtools/Loader.jsm", {})
 const { require } = devtools;
 
 this.sourceMap = require("source-map");
-this.acorn = require("acorn");
+this.acorn = require("acorn/acorn");
 this.prettyFast = require("devtools/pretty-fast");
 const { console } = Cu.import("resource://gre/modules/devtools/Console.jsm", {});
 
diff --git a/toolkit/devtools/server/actors/pretty-print-worker.js b/toolkit/devtools/server/actors/pretty-print-worker.js
index 07fad4eaafe7..b209ba2dd9bd 100644
--- a/toolkit/devtools/server/actors/pretty-print-worker.js
+++ b/toolkit/devtools/server/actors/pretty-print-worker.js
@@ -27,7 +27,7 @@
  *     { id, error }
  */
 
-importScripts("resource://gre/modules/devtools/acorn.js");
+importScripts("resource://gre/modules/devtools/acorn/acorn.js");
 importScripts("resource://gre/modules/devtools/source-map.js");
 importScripts("resource://gre/modules/devtools/pretty-fast.js");