diff --git a/dom/devicestorage/DeviceStorage.h b/dom/devicestorage/DeviceStorage.h
index f5c01e7eda2..89d238dca7f 100644
--- a/dom/devicestorage/DeviceStorage.h
+++ b/dom/devicestorage/DeviceStorage.h
@@ -50,6 +50,9 @@ private:
                              bool aEditable, 
                              nsIDOMDeviceStorageCursor** aRetval);
 
+  static bool IsMimeTypeCorrectForStorageType(nsAString& aType,
+					      nsIDOMBlob* aBlob);
+
   nsString mStorageType;
   nsCOMPtr<nsIFile> mRootDirectory;
 
diff --git a/dom/devicestorage/nsDeviceStorage.cpp b/dom/devicestorage/nsDeviceStorage.cpp
index 2db2d135dd2..a2e4838caca 100644
--- a/dom/devicestorage/nsDeviceStorage.cpp
+++ b/dom/devicestorage/nsDeviceStorage.cpp
@@ -39,6 +39,8 @@
 #include "nsIMIMEService.h"
 #include "nsCExternalHandlerService.h"
 
+#include "nsIStringBundle.h"
+
 // Microsoft's API Name hackery sucks
 #undef CreateEvent
 
@@ -47,11 +49,7 @@
 #include "nsIVolumeService.h"
 #endif
 
-#define DEBUG_ISTYPE 1
-
-#ifdef DEBUG_ISTYPE
-#include "nsIConsoleService.h"
-#endif
+#define DEVICESTORAGE_PROPERTIES "chrome://global/content/devicestorage.properties"
 
 using namespace mozilla::dom;
 using namespace mozilla::dom::devicestorage;
@@ -84,7 +82,9 @@ private:
   nsCString mType;
 };
 
-DeviceStorageFile::DeviceStorageFile(const nsAString& aStorageType, nsIFile* aFile, const nsAString& aPath)
+DeviceStorageFile::DeviceStorageFile(const nsAString& aStorageType,
+				     nsIFile* aFile,
+				     const nsAString& aPath)
   : mPath(aPath)
   , mStorageType(aStorageType)
   , mEditable(false)
@@ -155,61 +155,38 @@ DeviceStorageFile::IsType(nsAString& aType)
 {
   NS_ASSERTION(NS_IsMainThread(), "Wrong thread!");
 
-#ifdef DEBUG_ISTYPE
-  nsCOMPtr<nsIConsoleService> svc = do_GetService(NS_CONSOLESERVICE_CONTRACTID);
-  char buffer[1024];
-  nsCString path;
-  mFile->GetNativePath(path);
-
-  PRIntervalTime iStart = PR_IntervalNow();
-#endif
-
-  nsAutoCString mimeType;
-  nsCOMPtr<nsIMIMEService> mimeService = do_GetService(NS_MIMESERVICE_CONTRACTID);
-  if (!mimeService) {
+  // String bundles are cached by the bundle service.
+  nsCOMPtr<nsIStringBundleService> stringService = mozilla::services::GetStringBundleService();
+  if (!stringService) {
     return false;
   }
 
-  nsresult rv = mimeService->GetTypeFromFile(mFile, mimeType);
-  if (NS_FAILED(rv)) {
-#ifdef DEBUG_ISTYPE
-    sprintf(buffer, "GetTypeFromFile failed for %s (took: %dms)\n",
-	    path.get(),
-	    PR_IntervalToMilliseconds(PR_IntervalNow() - iStart));
-
-    nsString data;
-    CopyASCIItoUTF16(buffer, data);
-    svc->LogStringMessage(data.get());
-    printf("%s\n", buffer);
-#endif
+  nsCOMPtr<nsIStringBundle> filterBundle;
+  if (NS_FAILED(stringService->CreateBundle(DEVICESTORAGE_PROPERTIES,
+					    getter_AddRefs(filterBundle)))) {
     return false;
   }
 
-#ifdef DEBUG_ISTYPE
-  sprintf(buffer, "IsType of %s is %s (took: %dms)\n",
-	  path.get(),
-	  mimeType.get(),
-	  PR_IntervalToMilliseconds(PR_IntervalNow() - iStart));
+  nsString path;
+  mFile->GetPath(path);
 
-  nsString data;
-  CopyASCIItoUTF16(buffer, data);
-  svc->LogStringMessage(data.get());
-  printf("%s\n", buffer);
-#endif
-
-  if (aType.Equals(NS_LITERAL_STRING("pictures"))) {
-    return StringBeginsWith(mimeType, NS_LITERAL_CSTRING("image/"));
+  int32_t dotIdx = path.RFindChar(PRUnichar('.'));
+  if (dotIdx == kNotFound) {
+    return false;
   }
 
-  if (aType.Equals(NS_LITERAL_STRING("videos"))) {
-    return StringBeginsWith(mimeType, NS_LITERAL_CSTRING("video/"));
+  nsAutoString extensionMatch;
+  extensionMatch.AssignASCII("*");
+  extensionMatch.Append(Substring(path, dotIdx));
+  extensionMatch.AppendASCII(";");
+
+  nsString extensionListStr;
+  if (NS_FAILED(filterBundle->GetStringFromName(aType.BeginReading(),
+						getter_Copies(extensionListStr)))) {
+    return false;
   }
 
-  if (aType.Equals(NS_LITERAL_STRING("music"))) {
-    return StringBeginsWith(mimeType, NS_LITERAL_CSTRING("audio/"));
-  }
-
-  return false;
+  return FindInReadable(extensionMatch, extensionListStr);
 }
 
 void
@@ -343,7 +320,7 @@ DeviceStorageFile::Remove()
   if (NS_FAILED(rv)) {
     return rv;
   }
-  
+
   if (!check) {
     return NS_OK;
   }
@@ -1565,17 +1542,65 @@ nsDOMDeviceStorage::CreateDeviceStoragesFor(nsPIDOMWindow* aWin,
   }
 }
 
+bool
+nsDOMDeviceStorage::IsMimeTypeCorrectForStorageType(nsAString& aType, nsIDOMBlob* aBlob)
+{
+  NS_ASSERTION(aBlob, "Calling IsMimeTypeCorrectForStorageType without a blob");
+
+  nsString mimeType;
+  if (NS_FAILED(aBlob->GetType(mimeType))) {
+    return false;
+  }
+
+  if (aType.Equals(NS_LITERAL_STRING("pictures"))) {
+    return StringBeginsWith(mimeType, NS_LITERAL_STRING("image/"));
+  }
+
+  if (aType.Equals(NS_LITERAL_STRING("videos"))) {
+    return StringBeginsWith(mimeType, NS_LITERAL_STRING("video/"));
+  }
+
+  if (aType.Equals(NS_LITERAL_STRING("music"))) {
+    return StringBeginsWith(mimeType, NS_LITERAL_STRING("audio/"));
+  }
+
+  return false;
+}
+
 NS_IMETHODIMP
 nsDOMDeviceStorage::Add(nsIDOMBlob *aBlob, nsIDOMDOMRequest * *_retval)
 {
+  if (!aBlob) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIMIMEService> mimeSvc = do_GetService(NS_MIMESERVICE_CONTRACTID);
+  if (!mimeSvc) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // if mimeType isn't set, we will not get a correct
+  // extension, and AddNamed() will fail.  This will post an
+  // onerror to the requestee.
+  nsString mimeType;
+  aBlob->GetType(mimeType);
+
+  nsCString extension;
+  mimeSvc->GetPrimaryExtension(NS_LossyConvertUTF16toASCII(mimeType), EmptyCString(), extension);
+  // if extension is null here, we will ignore it for now.
+  // AddNamed() will check the file path and fail.  This
+  // will post an onerror to the requestee.
+
   // possible race here w/ unique filename
   char buffer[128];
-  NS_MakeRandomString(buffer, 128);
+  NS_MakeRandomString(buffer, ArrayLength(buffer));
 
-  nsString path;
-  path.AssignWithConversion(nsDependentCString(buffer));
+  nsAutoCString path;
+  path.Assign(nsDependentCString(buffer));
+  path.Append(".");
+  path.Append(extension);
 
-  return AddNamed(aBlob, path, _retval);
+  return AddNamed(aBlob, NS_ConvertASCIItoUTF16(path), _retval);
 }
 
 NS_IMETHODIMP
@@ -1598,14 +1623,17 @@ nsDOMDeviceStorage::AddNamed(nsIDOMBlob *aBlob,
   nsCOMPtr<nsIRunnable> r;
 
   nsRefPtr<DeviceStorageFile> dsf = new DeviceStorageFile(mStorageType, mRootDirectory, aPath);
-
-  if (!dsf->IsSafePath()) {
+  if (!dsf->IsType(mStorageType) || !IsMimeTypeCorrectForStorageType(mStorageType, aBlob)) {
+    r = new PostErrorEvent(request, POST_ERROR_EVENT_ILLEGAL_TYPE, dsf);
+  }
+  else if (!dsf->IsSafePath()) {
     r = new PostErrorEvent(request, POST_ERROR_EVENT_ILLEGAL_FILE_NAME, dsf);
   }
   else {
     r = new DeviceStorageRequest(DeviceStorageRequest::DEVICE_STORAGE_REQUEST_WRITE,
-                                 win, mPrincipal, dsf, request, aBlob);
+				 win, mPrincipal, dsf, request, aBlob);
   }
+
   NS_DispatchToMainThread(r);
   return NS_OK;
 }
@@ -1655,7 +1683,6 @@ nsDOMDeviceStorage::GetInternal(const JS::Value & aPath,
 
   nsRefPtr<DeviceStorageFile> dsf = new DeviceStorageFile(mStorageType, mRootDirectory, path);
   dsf->SetEditable(aEditable);
-
   if (!dsf->IsSafePath()) {
     r = new PostErrorEvent(request, POST_ERROR_EVENT_ILLEGAL_FILE_NAME, dsf);
   } else {
diff --git a/dom/devicestorage/nsDeviceStorage.h b/dom/devicestorage/nsDeviceStorage.h
index b5c1f5e5797..260faec8063 100644
--- a/dom/devicestorage/nsDeviceStorage.h
+++ b/dom/devicestorage/nsDeviceStorage.h
@@ -33,6 +33,7 @@ class nsPIDOMWindow;
 #define POST_ERROR_EVENT_FILE_NOT_ENUMERABLE         "File location is not enumerable"
 #define POST_ERROR_EVENT_PERMISSION_DENIED           "Permission Denied"
 #define POST_ERROR_EVENT_ILLEGAL_FILE_NAME           "Illegal file name"
+#define POST_ERROR_EVENT_ILLEGAL_TYPE                "Illegal content type"
 #define POST_ERROR_EVENT_UNKNOWN                     "Unknown"
 #define POST_ERROR_EVENT_NON_STRING_TYPE_UNSUPPORTED "Non-string type unsupported"
 #define POST_ERROR_EVENT_NOT_IMPLEMENTED             "Not implemented"
diff --git a/dom/devicestorage/test/Makefile.in b/dom/devicestorage/test/Makefile.in
index f029a097d8b..e26cffb59eb 100644
--- a/dom/devicestorage/test/Makefile.in
+++ b/dom/devicestorage/test/Makefile.in
@@ -10,8 +10,12 @@ relativesrcdir	= @relativesrcdir@
 
 include $(DEPTH)/config/autoconf.mk
 
+#  man, our mime database sucks hard.  followup bug # 788273
+#		test_add.html \
+
 MOCHITEST_FILES	= \
 		test_sanity.html \
+		test_addCorrectType.html \
 		test_basic.html \
 		test_enumerate.html \
 		test_enumerateMultipleContinue.html \
diff --git a/dom/devicestorage/test/test_add.html b/dom/devicestorage/test/test_add.html
new file mode 100644
index 00000000000..2e1bd6edb21
--- /dev/null
+++ b/dom/devicestorage/test/test_add.html
@@ -0,0 +1,68 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=786922
+-->
+<head>
+  <title>Test for basic sanity of the device storage API </title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="devicestorage_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=786922">Mozilla Bug 786922</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+
+devicestorage_setup();
+
+function add(storage, mime) {
+  dump("adding: " + mime + "\n");
+  return navigator.getDeviceStorage(storage).add(createRandomBlob(mime));
+}
+
+var tests = [
+  function () { return add("pictures", "image/png")},
+  function () { return add("videos",   "video/webm")},
+  function () { return add("music",    "audio/wav")},
+];
+
+function fail(e) {
+  ok(false, "onerror was called");
+  devicestorage_cleanup();
+}
+
+function next(e) {
+
+  if (e != undefined)
+    ok(true, "addError was called");
+  
+  var f = tests.pop();
+
+  if (f == undefined) {
+    devicestorage_cleanup();
+    return;
+  }
+
+  request = f();
+  request.onsuccess = next;
+  request.onerror = fail;
+}
+
+next();
+
+</script>
+</pre>
+</body>
+</html>
+
diff --git a/dom/devicestorage/test/test_addCorrectType.html b/dom/devicestorage/test/test_addCorrectType.html
new file mode 100644
index 00000000000..2920840f91e
--- /dev/null
+++ b/dom/devicestorage/test/test_addCorrectType.html
@@ -0,0 +1,72 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=786922
+-->
+<head>
+  <title>Test for basic sanity of the device storage API </title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="devicestorage_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=786922">Mozilla Bug 786922</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+
+devicestorage_setup();
+
+function addNamed(storage, mime, fileExtension) {
+  dump("adding: " + mime + " " + fileExtension + "\n");
+  return navigator.getDeviceStorage(storage).addNamed(createRandomBlob(mime), randomFilename(40) + "." + fileExtension);
+}
+
+// These tests must all fail
+var tests = [
+  function () { return addNamed("pictures", "kyle/smash", ".png")},
+  function () { return addNamed("pictures", "image/png",  ".poo")},
+  function () { return addNamed("music",    "kyle/smash", ".mp3")},
+  function () { return addNamed("music",    "music/mp3",  ".poo")},
+  function () { return addNamed("videos",   "kyle/smash", ".ogv")},
+  function () { return addNamed("videos",   "video/ogv",  ".poo")},
+];
+
+function fail(e) {
+  ok(false, "addSuccess was called");
+  devicestorage_cleanup();
+}
+
+function next(e) {
+
+  if (e != undefined)
+    ok(true, "addError was called");
+  
+  var f = tests.pop();
+
+  if (f == undefined) {
+    devicestorage_cleanup();
+    return;
+  }
+
+  request = f();
+  request.onsuccess = fail;
+  request.onerror = next;
+}
+
+next();
+
+</script>
+</pre>
+</body>
+</html>
+