--- a/dom/devicestorage/DeviceStorage.h
+++ b/dom/devicestorage/DeviceStorage.h
@@ -244,16 +244,17 @@ public:
   already_AddRefed<DOMRequest> CreateFileDescriptor(const nsAString& aPath,
                                                     DeviceStorageFileDescriptor* aDSFD,
                                                     ErrorResult& aRv);
 
   bool CanBeMounted();
   bool CanBeFormatted();
   bool CanBeShared();
   bool IsRemovable();
+  bool LowDiskSpace();
   bool Default();
   void GetStorageName(nsAString& aStorageName);
 
   already_AddRefed<Promise>
   GetRoot(ErrorResult& aRv);
 
   static void
   CreateDeviceStorageFor(nsPIDOMWindow* aWin,

--- a/dom/devicestorage/DeviceStorageStatics.cpp
+++ b/dom/devicestorage/DeviceStorageStatics.cpp
@@ -67,16 +67,17 @@ DeviceStorageStatics::InitializeDirs()
   }
 
   MOZ_ASSERT(sInstance->mInitialized);
 }
 
 DeviceStorageStatics::DeviceStorageStatics()
   : mInitialized(false)
   , mPromptTesting(false)
+  , mLowDiskSpace(false)
 {
   DS_LOG_INFO("");
 }
 
 DeviceStorageStatics::~DeviceStorageStatics()
 {
   DS_LOG_INFO("");
 }
@@ -353,16 +354,26 @@ DeviceStorageStatics::IsPromptTesting()
 {
   StaticMutexAutoLock lock(sMutex);
   if (NS_WARN_IF(!sInstance)) {
     return false;
   }
   return sInstance->mPromptTesting;
 }
 
+/* static */ bool
+DeviceStorageStatics::LowDiskSpace()
+{
+  StaticMutexAutoLock lock(sMutex);
+  if (NS_WARN_IF(!sInstance)) {
+    return false;
+  }
+  return sInstance->mLowDiskSpace;
+}
+
 /* static */ void
 DeviceStorageStatics::GetWritableName(nsString& aName)
 {
   StaticMutexAutoLock lock(sMutex);
   if (NS_WARN_IF(!sInstance)) {
     aName.Truncate();
     return;
   }
@@ -600,37 +611,39 @@ DeviceStorageStatics::Observe(nsISupport
     while (i > 0) {
       --i;
       mListeners[i]->OnFileWatcherUpdate(data, file);
     }
     return NS_OK;
   }
 
   if (!strcmp(aTopic, kDiskSpaceWatcher)) {
-    // 'disk-space-watcher' notifications are sent when there is a modification
-    // of a file in a specific location while a low device storage situation
-    // exists or after recovery of a low storage situation. For Firefox OS,
-    // these notifications are specific for apps storage.
-    bool lowDiskSpace = false;
-    if (!NS_strcmp(aData, MOZ_UTF16("full"))) {
-      lowDiskSpace = true;
-    } else if (NS_strcmp(aData, MOZ_UTF16("free"))) {
-      return NS_OK;
-    }
-
     StaticMutexAutoLock lock(sMutex);
     if (NS_WARN_IF(!sInstance)) {
       return NS_OK;
     }
 
+    // 'disk-space-watcher' notifications are sent when there is a modification
+    // of a file in a specific location while a low device storage situation
+    // exists or after recovery of a low storage situation. For Firefox OS,
+    // these notifications are specific for apps storage.
+    if (!NS_strcmp(aData, MOZ_UTF16("full"))) {
+      sInstance->mLowDiskSpace = true;
+    } else if (!NS_strcmp(aData, MOZ_UTF16("free"))) {
+      sInstance->mLowDiskSpace = false;
+    } else {
+      return NS_OK;
+    }
+
+
     uint32_t i = mListeners.Length();
-    DS_LOG_INFO("disk space %d (%u)", lowDiskSpace, i);
+    DS_LOG_INFO("disk space %d (%u)", sInstance->mLowDiskSpace, i);
     while (i > 0) {
       --i;
-      mListeners[i]->OnDiskSpaceWatcher(lowDiskSpace);
+      mListeners[i]->OnDiskSpaceWatcher(sInstance->mLowDiskSpace);
     }
     return NS_OK;
   }
 
   if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
     StaticMutexAutoLock lock(sMutex);
     if (NS_WARN_IF(!sInstance)) {
       return NS_OK;

--- a/dom/devicestorage/DeviceStorageStatics.h
+++ b/dom/devicestorage/DeviceStorageStatics.h
@@ -25,16 +25,17 @@ public:
   NS_DECL_THREADSAFE_ISUPPORTS
   NS_DECL_NSIOBSERVER
 
   static void Initialize();
   static void InitializeDirs();
   static void AddListener(nsDOMDeviceStorage* aListener);
   static void RemoveListener(nsDOMDeviceStorage* aListener);
 
+  static bool LowDiskSpace();
   static bool IsPromptTesting();
   static void GetWritableName(nsString& aName);
   static void SetWritableName(const nsAString& aName);
 
   static bool HasOverrideRootDir();
   static already_AddRefed<nsIFile> GetAppsDir();
   static already_AddRefed<nsIFile> GetCrashesDir();
   static already_AddRefed<nsIFile> GetPicturesDir();
@@ -87,16 +88,17 @@ private:
     nsCOMPtr<nsIThread> mOwningThread;
   };
 
   nsTArray<nsRefPtr<ListenerWrapper> > mListeners;
   nsCOMPtr<nsIFile> mDirs[TYPE_COUNT];
 
   bool mInitialized;
   bool mPromptTesting;
+  bool mLowDiskSpace;
   nsString mWritableName;
 
   static StaticRefPtr<DeviceStorageStatics> sInstance;
   static StaticMutex sMutex;
 };
 
 } // namespace devicestorage
 } // namespace dom

--- a/dom/devicestorage/nsDeviceStorage.cpp
+++ b/dom/devicestorage/nsDeviceStorage.cpp
@@ -3369,16 +3369,22 @@ nsDOMDeviceStorage::CanBeShared()
 }
 
 bool
 nsDOMDeviceStorage::IsRemovable()
 {
   return mIsRemovable;
 }
 
+bool
+nsDOMDeviceStorage::LowDiskSpace()
+{
+  return DeviceStorageStatics::LowDiskSpace();
+}
+
 already_AddRefed<Promise>
 nsDOMDeviceStorage::GetRoot(ErrorResult& aRv)
 {
   if (!mFileSystem) {
     mFileSystem = new DeviceStorageFileSystem(mStorageType, mStorageName);
     mFileSystem->Init(this);
   }
   return mozilla::dom::Directory::GetRoot(mFileSystem, aRv);

--- a/dom/webidl/DeviceStorage.webidl
+++ b/dom/webidl/DeviceStorage.webidl
@@ -81,12 +81,15 @@ interface DeviceStorage : EventTarget {
 
   // Determines if this storage area is the one which will be used by default
   // for storing new files.
   readonly attribute boolean default;
 
   // Indicates if the storage area denoted by storageName is removable
   readonly attribute boolean isRemovable;
 
+  // True if the storage area is close to being full
+  readonly attribute boolean lowDiskSpace;
+
   [NewObject]
   // XXXbz what type does this really return?
   Promise<any> getRoot();
 };