diff --git a/dom/browser-element/BrowserElementChildPreload.js b/dom/browser-element/BrowserElementChildPreload.js
index 084edb5355c..df21a6fecbf 100644
--- a/dom/browser-element/BrowserElementChildPreload.js
+++ b/dom/browser-element/BrowserElementChildPreload.js
@@ -60,7 +60,7 @@ let CERTIFICATE_ERROR_PAGE_PREF = 'security.alternate_certificate_error_page';
 let NS_ERROR_MODULE_BASE_OFFSET = 0x45;
 let NS_ERROR_MODULE_SECURITY= 21;
 function NS_ERROR_GET_MODULE(err) {
-  return ((((err) >> 16) - NS_ERROR_MODULE_BASE_OFFSET) & 0x1fff) 
+  return ((((err) >> 16) - NS_ERROR_MODULE_BASE_OFFSET) & 0x1fff);
 }
 
 function NS_ERROR_GET_CODE(err) {
@@ -82,7 +82,7 @@ let SSL_ERROR_BAD_CERT_DOMAIN = (SSL_ERROR_BASE + 12);
 
 function getErrorClass(errorCode) {
   let NSPRCode = -1 * NS_ERROR_GET_CODE(errorCode);
- 
+
   switch (NSPRCode) {
     case SEC_ERROR_UNKNOWN_ISSUER:
     case SEC_ERROR_CA_CERT_INVALID:
@@ -129,6 +129,9 @@ function BrowserElementChild() {
 
   this._nextPaintHandler = null;
 
+  this._isContentWindowCreated = false;
+  this._pendingSetInputMethodActive = [];
+
   this._init();
 };
 
@@ -566,6 +569,11 @@ BrowserElementChild.prototype = {
       this._addMozAfterPaintHandler(function () {
         sendAsyncMsg('documentfirstpaint');
       });
+      this._isContentWindowCreated = true;
+      // Handle pending SetInputMethodActive request.
+      while (this._pendingSetInputMethodActive.length > 0) {
+        this._recvSetInputMethodActive(this._pendingSetInputMethodActive.shift());
+      }
     }
   },
 
@@ -904,6 +912,17 @@ BrowserElementChild.prototype = {
 
   _recvSetInputMethodActive: function(data) {
     let msgData = { id: data.json.id };
+    if (!this._isContentWindowCreated) {
+      if (data.json.args.isActive) {
+        // To activate the input method, we should wait before the content
+        // window is ready.
+        this._pendingSetInputMethodActive.push(data);
+        return;
+      }
+      sendAsyncMsg('got-set-input-method-active', msgData);
+      msgData.successRv = null;
+      return;
+    }
     // Unwrap to access webpage content.
     let nav = XPCNativeWrapper.unwrap(content.document.defaultView.navigator);
     if (nav.mozInputMethod) {
@@ -977,7 +996,7 @@ BrowserElementChild.prototype = {
           return;
         }
 
-        if (NS_ERROR_GET_MODULE(status) == NS_ERROR_MODULE_SECURITY && 
+        if (NS_ERROR_GET_MODULE(status) == NS_ERROR_MODULE_SECURITY &&
             getErrorClass(status) == Ci.nsINSSErrorsService.ERROR_CLASS_BAD_CERT) {
 
           // XXX Is there a point firing the event if the error page is not
diff --git a/dom/inputmethod/mochitest/file_inputmethod.html b/dom/inputmethod/mochitest/file_inputmethod.html
new file mode 100644
index 00000000000..f228a8d8d12
--- /dev/null
+++ b/dom/inputmethod/mochitest/file_inputmethod.html
@@ -0,0 +1,18 @@
+<html>
+<body>
+<script>
+  var im = navigator.mozInputMethod;
+  if (im) {
+    // Automatically append location hash to current input field.
+    im.oninputcontextchange = function() {
+      var ctx = im.inputcontext;
+      if (ctx) {
+        intervalId = setTimeout(function() {
+          ctx.replaceSurroundingText(location.hash);
+        }, 0);
+      }
+    };
+  }
+</script>
+</body>
+</html>
diff --git a/dom/inputmethod/mochitest/mochitest.ini b/dom/inputmethod/mochitest/mochitest.ini
index 84c391c2eb6..84f79fcd7c9 100644
--- a/dom/inputmethod/mochitest/mochitest.ini
+++ b/dom/inputmethod/mochitest/mochitest.ini
@@ -2,6 +2,8 @@
 support-files =
   inputmethod_common.js
   file_test_app.html
+  file_inputmethod.html
 
 [test_basic.html]
+[test_bug944397.html]
 
diff --git a/dom/inputmethod/mochitest/test_bug944397.html b/dom/inputmethod/mochitest/test_bug944397.html
new file mode 100644
index 00000000000..e7f7fba56dc
--- /dev/null
+++ b/dom/inputmethod/mochitest/test_bug944397.html
@@ -0,0 +1,89 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=944397
+-->
+<head>
+  <title>Basic test for InputMethod API.</title>
+  <script type="application/javascript;version=1.7" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript;version=1.7" src="inputmethod_common.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=944397">Mozilla Bug 944397</a>
+<input type="text" />
+<p id="display"></p>
+<pre id="test">
+<script class="testbody" type="application/javascript;version=1.7">
+
+inputmethod_setup(function() {
+  runTest();
+});
+
+// The frame script running in file_test_app.html.
+function appFrameScript() {
+  let input = content.document.getElementById('test-input');
+  input.oninput = function() {
+    sendAsyncMessage('test:InputMethod:oninput', {});
+  };
+}
+
+function runTest() {
+  var timeoutId = null;
+
+  // Create an app frame to recieve keyboard inputs.
+  let app = document.createElement('iframe');
+  app.src = 'file_test_app.html';
+  app.setAttribute('mozbrowser', true);
+  document.body.appendChild(app);
+  app.addEventListener('mozbrowserloadend', function() {
+    let mm = SpecialPowers.getBrowserFrameMessageManager(app);
+    mm.loadFrameScript('data:,(' + appFrameScript.toString() + ')();', false);
+    mm.addMessageListener("test:InputMethod:oninput", function() {
+      ok(true, 'Keyboard input was received.');
+      clearTimeout(timeoutId);
+      inputmethod_cleanup();
+    });
+  });
+
+  // Create a browser frame to load the input method app.
+  let keyboard = document.createElement('iframe');
+  keyboard.setAttribute('mozbrowser', true);
+  document.body.appendChild(keyboard);
+
+  let path = location.pathname;
+  let imeUrl = location.protocol + '//' + location.host +
+               path.substring(0, path.lastIndexOf('/')) +
+               '/file_inputmethod.html#data';
+  SpecialPowers.pushPermissions([{
+    type: 'input',
+    allow: true,
+    context: imeUrl
+  }], function() {
+     let req = keyboard.setInputMethodActive(true);
+
+     req.onsuccess = function() {
+       ok(true, 'setInputMethodActive succeeded.');
+       timeoutId = setTimeout(function() {
+        inputmethod_cleanup();
+        ok(false, 'Failed to generate keyboard input.');
+       }, 60000);
+     };
+
+     req.onerror = function() {
+       ok(false, 'setInputMethodActive failed: ' + this.error.name);
+       inputmethod_cleanup();
+     };
+
+     // Loads the input method app to the browser frame after a delay.
+     setTimeout(function() {
+       keyboard.src = imeUrl;
+     }, 100);
+  });
+}
+
+</script>
+</pre>
+</body>
+</html>
+
