--- a/devtools/client/webconsole/test/browser_webconsole_output_05.js
+++ b/devtools/client/webconsole/test/browser_webconsole_output_05.js
@@ -128,24 +128,24 @@ var inputTests = [
     output: 'Promise { <state>: "pending", foo: 1 }',
     printOutput: "[object Promise]",
     inspectable: true,
     variablesViewLabel: "Promise"
   },
 
   // 13
   {
-    input: "new Object({1: 'this\\nis\\nsupposed\\nto\\nbe\\na\\nvery" +
+    input: "new Object({0: 'this\\nis\\nsupposed\\nto\\nbe\\na\\nvery" +
            "\\nlong\\nstring\\n,shown\\non\\na\\nsingle\\nline', " +
-           "2: 'a shorter string', 3: 100})",
-    output: '[ <1 empty slot>, "this is supposed to be a very long ' + ELLIPSIS +
+           "1: 'a shorter string', 2: 100})",
+    output: '[ "this is supposed to be a very long ' + ELLIPSIS +
             '", "a shorter string", 100 ]',
     printOutput: "[object Object]",
     inspectable: true,
-    variablesViewLabel: "Object[4]"
+    variablesViewLabel: "Object[3]"
   },
 
   // 14
   {
     input: "new Proxy({a:1},[1,2,3])",
     output: 'Proxy { <target>: Object, <handler>: Array[3] }',
     printOutput: "[object Object]",
     inspectable: true,

--- a/devtools/client/webconsole/test/browser_webconsole_output_06.js
+++ b/devtools/client/webconsole/test/browser_webconsole_output_06.js
@@ -125,145 +125,91 @@ var inputTests = [
     output: 'Object [ "a", "b" ]',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object[2]",
   },
 
   // 14
   {
-    input: '({0: "a", 42: "b"})',
-    output: '[ "a", <9 empty slots>, 33 more\u2026 ]',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object[43]",
-  },
-
-  // 15
-  {
     input: '({0: "a", 1: "b", 2: "c", 3: "d", 4: "e", 5: "f", 6: "g", ' +
            '7: "h", 8: "i", 9: "j", 10: "k", 11: "l"})',
     output: 'Object [ "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", ' +
             "2 more\u2026 ]",
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object[12]",
   },
 
-  // 16
+  // 15
   {
     input: '({0: "a", 1: "b", 2: "c", 3: "d", 4: "e", 5: "f", 6: "g", ' +
            '7: "h", 8: "i", 9: "j", 10: "k", 11: "l", m: "n"})',
     output: 'Object { 0: "a", 1: "b", 2: "c", 3: "d", 4: "e", 5: "f", ' +
             '6: "g", 7: "h", 8: "i", 9: "j", 3 more\u2026 }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 17
+  // 16
   {
     input: '({" ": "a"})',
     output: 'Object {  : "a" }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 18
+  // 17
   {
     input: '({})',
     output: 'Object {  }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 19
-  {
-    input: '({length: 0})',
-    output: 'Object [  ]',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object[0]",
-  },
-
-  // 20
-  {
-    input: '({length: 1})',
-    output: '[ <1 empty slot> ]',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object[1]",
-  },
-
-  // 21
-  {
-    input: '({0: "a", 1: "b", length: 1})',
-    output: 'Object { 0: "a", 1: "b", length: 1 }',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object",
-  },
-
-  // 22
+  // 18
   {
     input: '({0: "a", 1: "b", length: 2})',
     output: 'Object [ "a", "b" ]',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object[2]",
   },
 
-  // 23
-  {
-    input: '({0: "a", 1: "b", length: 3})',
-    output: '[ "a", "b", <1 empty slot> ]',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object[3]",
-  },
-
-  // 24
+  // 19
   {
     input: '({0: "a", 2: "b", length: 2})',
     output: 'Object { 0: "a", 2: "b", length: 2 }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 25
-  {
-    input: '({0: "a", 2: "b", length: 3})',
-    output: '[ "a", <1 empty slot>, "b" ]',
-    printOutput: "[object Object]",
-    inspectable: true,
-    variablesViewLabel: "Object[3]",
-  },
-
-  // 26
+  // 20
   {
     input: '({0: "a", b: "b", length: 1})',
     output: 'Object { 0: "a", b: "b", length: 1 }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 27
+  // 21
   {
     input: '({0: "a", b: "b", length: 2})',
     output: 'Object { 0: "a", b: "b", length: 2 }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 
-  // 28
+  // 22
   {
     input: '({42: "a"})',
     output: 'Object { 42: "a" }',
     printOutput: "[object Object]",
     inspectable: true,
     variablesViewLabel: "Object",
   },
 ];

--- a/devtools/server/actors/object.js
+++ b/devtools/server/actors/object.js
@@ -1936,33 +1936,41 @@ DebuggerServer.ObjectActorPreviewers.Obj
   function PseudoArray({obj, hooks}, grip, rawObj) {
     let length;
 
     let keys = obj.getOwnPropertyNames();
     if (keys.length == 0) {
       return false;
     }
 
-    // If no item is going to be displayed in preview, better display as sparse object.
-    // The first key should contain the smallest integer index (if any).
-    if (keys[0] >= OBJECT_PREVIEW_MAX_ITEMS) {
+    // We don't want to represent Objects as sparse arrays, so every property
+    // should match its index, or be the length property.
+    if (keys.some((key, i) => parseInt(key, 10) !== i && key !== "length")) {
       return false;
     }
 
     // Pseudo-arrays should only have array indices and, optionally, a "length" property.
     // Since integer indices are sorted first, check if the last property is "length".
     if (keys[keys.length - 1] === "length") {
       keys.pop();
       length = DevToolsUtils.getProperty(obj, "length");
     } else {
       // Otherwise, let length be the (presumably) greatest array index plus 1.
       length = +keys[keys.length - 1] + 1;
     }
-    // Check if length is a valid array length, i.e. is a Uint32 number.
-    if (typeof length !== "number" || length >>> 0 !== length) {
+
+    // If they are no numeric keys, or if the length does not represent the actual
+    // object length, or is not a valid array length, i.e. is a Uint32 number,
+    // do not label the object as ArrayLike.
+    if (
+      keys.length === 0 ||
+      keys.length !== length ||
+      typeof length !== "number" ||
+      length >>> 0 !== length
+    ) {
       return false;
     }
 
     // Ensure all keys are increasing array indices smaller than length. The order is not
     // guaranteed for exotic objects but, in most cases, big array indices and properties
     // which are not integer indices should be at the end. Then, iterating backwards
     // allows us to return earlier when the object is not completely a pseudo-array.
     let prev = length;

new file mode 100644
--- /dev/null
+++ b/devtools/server/tests/unit/test_objectgrips-array-like-object.js
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that objects are labeled as ArrayLike only when they have sequential
+// numeric keys, and if they have a length property, that it matches the number
+// of numeric keys. (See Bug 1371936)
+
+async function run_test() {
+  do_test_pending();
+  await run_test_with_server(DebuggerServer);
+  await run_test_with_server(WorkerDebuggerServer);
+  do_test_finished();
+}
+
+async function run_test_with_server(server) {
+  initTestDebuggerServer(server);
+  const debuggee = addTestGlobal("test-grips", server);
+  debuggee.eval(function stopMe(arg1) {
+    debugger;
+  }.toString());
+
+  const dbgClient = new DebuggerClient(server.connectPipe());
+  await dbgClient.connect();
+  const [,, threadClient] = await attachTestTabAndResume(dbgClient, "test-grips");
+
+  // Currying test function so we don't have to pass the debuggee and clients
+  const isArrayLike = object => test_object_grip_is_array_like(
+    debuggee, dbgClient, threadClient, object);
+
+  equal(await isArrayLike({}), false, "An empty object is not ArrayLike");
+  equal(await isArrayLike({length: 0}), false,
+    "An object with only a length property is not ArrayLike");
+  equal(await isArrayLike({2: "two"}), false,
+    "Object not starting at 0 is not ArrayLike");
+  equal(await isArrayLike({0: "zero", 2: "two"}), false,
+    "Object with non-consecutive numeric keys is not ArrayLike");
+  equal(await isArrayLike({0: "zero", 2: "two", length: 2}), false,
+    "Object with non-consecutive numeric keys is not ArrayLike");
+  equal(await isArrayLike({0: "zero", 1: "one", 2: "two", three: 3}), false,
+    "Object with a non-numeric property other than `length` is not ArrayLike");
+  equal(await isArrayLike({0: "zero", 1: "one", 2: "two", three: 3, length: 3}), false,
+    "Object with a non-numeric property other than `length` is not ArrayLike");
+  equal(await isArrayLike({0: "zero", 1: "one", 2: "two", length: 30}), false,
+    "Object with a wrongful `length` property is not ArrayLike");
+
+  equal(await isArrayLike({0: "zero"}), true);
+  equal(await isArrayLike({0: "zero", 1: "two"}), true);
+  equal(await isArrayLike({0: "zero", 1: "one", 2: "two", length: 3}), true);
+
+  await dbgClient.close();
+}
+
+async function test_object_grip_is_array_like(debuggee, dbgClient, threadClient, object) {
+  return new Promise((resolve, reject) => {
+    threadClient.addOneTimeListener("paused", async function (event, packet) {
+      let [grip] = packet.frame.arguments;
+      await threadClient.resume();
+      resolve(grip.preview.kind === "ArrayLike");
+    });
+
+    debuggee.eval(`
+      stopMe(${JSON.stringify(object)});
+    `);
+  });
+}

--- a/devtools/server/tests/unit/xpcshell.ini
+++ b/devtools/server/tests/unit/xpcshell.ini
@@ -172,16 +172,17 @@ reason = only ran on B2G
 [test_objectgrips-13.js]
 [test_objectgrips-14.js]
 [test_objectgrips-15.js]
 [test_objectgrips-16.js]
 [test_objectgrips-17.js]
 [test_objectgrips-18.js]
 [test_objectgrips-19.js]
 [test_objectgrips-20.js]
+[test_objectgrips-array-like-object.js]
 [test_promise_state-01.js]
 [test_promise_state-02.js]
 [test_promise_state-03.js]
 [test_interrupt.js]
 [test_stepping-01.js]
 [test_stepping-02.js]
 [test_stepping-03.js]
 [test_stepping-04.js]