new file mode 100644
--- /dev/null
+++ b/browser/devtools/shared/test/unit/test_VariablesView_getString_promise.js
@@ -0,0 +1,75 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const Cu = Components.utils;
+const { devtools } = Cu.import("resource://gre/modules/devtools/Loader.jsm", {});
+const { VariablesView } = Cu.import("resource:///modules/devtools/VariablesView.jsm", {});
+
+const PENDING = {
+  "type": "object",
+  "class": "Promise",
+  "actor": "conn0.pausedobj35",
+  "extensible": true,
+  "frozen": false,
+  "sealed": false,
+  "promiseState": {
+    "state": "pending"
+  },
+  "preview": {
+    "kind": "Object",
+    "ownProperties": {},
+    "ownPropertiesLength": 0,
+    "safeGetterValues": {}
+  }
+};
+
+const FULFILLED = {
+  "type": "object",
+  "class": "Promise",
+  "actor": "conn0.pausedobj35",
+  "extensible": true,
+  "frozen": false,
+  "sealed": false,
+  "promiseState": {
+    "state": "fulfilled",
+    "value": 10
+  },
+  "preview": {
+    "kind": "Object",
+    "ownProperties": {},
+    "ownPropertiesLength": 0,
+    "safeGetterValues": {}
+  }
+};
+
+const REJECTED = {
+  "type": "object",
+  "class": "Promise",
+  "actor": "conn0.pausedobj35",
+  "extensible": true,
+  "frozen": false,
+  "sealed": false,
+  "promiseState": {
+    "state": "rejected",
+    "reason": 10
+  },
+  "preview": {
+    "kind": "Object",
+    "ownProperties": {},
+    "ownPropertiesLength": 0,
+    "safeGetterValues": {}
+  }
+};
+
+function run_test() {
+  equal(VariablesView.getString(PENDING, { concise: true }), "Promise");
+  equal(VariablesView.getString(PENDING),                    'Promise {<state>: "pending"}');
+
+  equal(VariablesView.getString(FULFILLED, { concise: true }), "Promise");
+  equal(VariablesView.getString(FULFILLED),                    'Promise {<state>: "fulfilled", <value>: 10}');
+
+  equal(VariablesView.getString(REJECTED, { concise: true }), "Promise");
+  equal(VariablesView.getString(REJECTED),                    'Promise {<state>: "rejected", <reason>: 10}');
+}

--- a/browser/devtools/shared/test/unit/xpcshell.ini
+++ b/browser/devtools/shared/test/unit/xpcshell.ini
@@ -2,8 +2,9 @@
 head =
 tail =
 firefox-appdir = browser
 skip-if = toolkit == 'android' || toolkit == 'gonk'
 
 [test_bezierCanvas.js]
 [test_cubicBezier.js]
 [test_undoStack.js]
+[test_VariablesView_getString_promise.js]
\ No newline at end of file

--- a/browser/devtools/shared/widgets/VariablesView.jsm
+++ b/browser/devtools/shared/widgets/VariablesView.jsm
@@ -3570,16 +3570,27 @@ VariablesView.stringifiers.byObjectKind 
   // Stringifier for any kind of object.
   Object: function(aGrip, {concise}) {
     if (concise) {
       return aGrip.class;
     }
 
     let {preview} = aGrip;
     let props = [];
+
+    if (aGrip.class == "Promise" && aGrip.promiseState) {
+      let { state, value, reason } = aGrip.promiseState;
+      props.push("<state>: " + VariablesView.getString(state));
+      if (state == "fulfilled") {
+        props.push("<value>: " + VariablesView.getString(value, { concise: true }));
+      } else if (state == "rejected") {
+        props.push("<reason>: " + VariablesView.getString(reason, { concise: true }));
+      }
+    }
+
     for (let key of Object.keys(preview.ownProperties || {})) {
       let value = preview.ownProperties[key];
       let valueString = "";
       if (value.get) {
         valueString = "Getter";
       } else if (value.set) {
         valueString = "Setter";
       } else {