diff --git a/dom/system/gonk/mozstumbler/UploadStumbleRunnable.cpp b/dom/system/gonk/mozstumbler/UploadStumbleRunnable.cpp
index 09f0834e341c..963109cb5397 100644
--- a/dom/system/gonk/mozstumbler/UploadStumbleRunnable.cpp
+++ b/dom/system/gonk/mozstumbler/UploadStumbleRunnable.cpp
@@ -7,14 +7,15 @@
 #include "UploadStumbleRunnable.h"
 #include "StumblerLogging.h"
 #include "mozilla/dom/Event.h"
+#include "nsIInputStream.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsIURLFormatter.h"
 #include "nsIVariant.h"
 #include "nsIXMLHttpRequest.h"
 #include "nsNetUtil.h"
 
-UploadStumbleRunnable::UploadStumbleRunnable(const nsACString& aUploadData)
-: mUploadData(aUploadData)
+UploadStumbleRunnable::UploadStumbleRunnable(nsIInputStream* aUploadData)
+: mUploadInputStream(aUploadData)
 {
 }
 
@@ -36,7 +37,7 @@ UploadStumbleRunnable::Upload()
   nsCOMPtr<nsIWritableVariant> variant = do_CreateInstance("@mozilla.org/variant;1", &rv);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  rv = variant->SetAsACString(mUploadData);
+  rv = variant->SetAsISupports(mUploadInputStream);
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsCOMPtr<nsIXMLHttpRequest> xhr = do_CreateInstance(NS_XMLHTTPREQUEST_CONTRACTID, &rv);
@@ -63,13 +64,13 @@ UploadStumbleRunnable::Upload()
   rv = xhr->Open(NS_LITERAL_CSTRING("POST"), NS_ConvertUTF16toUTF8(url), false, EmptyString(), EmptyString());
   NS_ENSURE_SUCCESS(rv, rv);
 
-  xhr->SetRequestHeader(NS_LITERAL_CSTRING("Content-Type"), NS_LITERAL_CSTRING("application/json"));
+  xhr->SetRequestHeader(NS_LITERAL_CSTRING("Content-Type"), NS_LITERAL_CSTRING("gzip"));
   xhr->SetMozBackgroundRequest(true);
   // 60s timeout
   xhr->SetTimeout(60 * 1000);
 
   nsCOMPtr<EventTarget> target(do_QueryInterface(xhr));
-  nsRefPtr<nsIDOMEventListener> listener = new UploadEventListener(xhr, mUploadData.Length());
+  nsRefPtr<nsIDOMEventListener> listener = new UploadEventListener(xhr);
 
   const char* const sEventStrings[] = {
     // nsIXMLHttpRequestEventTarget event types
@@ -93,8 +94,8 @@ UploadStumbleRunnable::Upload()
 
 NS_IMPL_ISUPPORTS(UploadEventListener, nsIDOMEventListener)
 
-UploadEventListener::UploadEventListener(nsIXMLHttpRequest* aXHR, int64_t aFileSize)
-: mXHR(aXHR), mFileSize(aFileSize)
+UploadEventListener::UploadEventListener(nsIXMLHttpRequest* aXHR)
+: mXHR(aXHR)
 {
 }
 
@@ -109,7 +110,7 @@ UploadEventListener::HandleEvent(nsIDOMEvent* aEvent)
   }
 
   if (type.EqualsLiteral("load")) {
-    STUMBLER_DBG("Got load Event : size %lld", mFileSize);
+    STUMBLER_DBG("Got load Event\n");
   } else if (type.EqualsLiteral("error") && mXHR) {
     STUMBLER_ERR("Upload Error");
   } else {
diff --git a/dom/system/gonk/mozstumbler/UploadStumbleRunnable.h b/dom/system/gonk/mozstumbler/UploadStumbleRunnable.h
index e05dc4409be9..a9ea83e37dbe 100644
--- a/dom/system/gonk/mozstumbler/UploadStumbleRunnable.h
+++ b/dom/system/gonk/mozstumbler/UploadStumbleRunnable.h
@@ -11,6 +11,7 @@
 #include "nsIDOMEventListener.h"
 
 class nsIXMLHttpRequest;
+class nsIInputStream;
 
 /*
  This runnable is managed by WriteStumbleOnThread only, see that class
@@ -19,12 +20,12 @@ class nsIXMLHttpRequest;
 class UploadStumbleRunnable final : public nsRunnable
 {
 public:
-  explicit UploadStumbleRunnable(const nsACString& aUploadData);
+  explicit UploadStumbleRunnable(nsIInputStream* aUploadInputStream);
 
   NS_IMETHOD Run() override;
 private:
   virtual ~UploadStumbleRunnable() {}
-  const nsCString mUploadData;
+  nsCOMPtr<nsIInputStream> mUploadInputStream;
   nsresult Upload();
 };
 
@@ -32,7 +33,7 @@ private:
 class UploadEventListener : public nsIDOMEventListener
 {
 public:
-  UploadEventListener(nsIXMLHttpRequest* aXHR, int64_t aFileSize);
+  UploadEventListener(nsIXMLHttpRequest* aXHR);
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSIDOMEVENTLISTENER
@@ -40,7 +41,6 @@ public:
 protected:
   virtual ~UploadEventListener() {}
   nsCOMPtr<nsIXMLHttpRequest> mXHR;
-  int64_t mFileSize;
 };
 
 #endif
diff --git a/dom/system/gonk/mozstumbler/WriteStumbleOnThread.cpp b/dom/system/gonk/mozstumbler/WriteStumbleOnThread.cpp
index 1cec6a5d4fb0..f5c59ec94099 100644
--- a/dom/system/gonk/mozstumbler/WriteStumbleOnThread.cpp
+++ b/dom/system/gonk/mozstumbler/WriteStumbleOnThread.cpp
@@ -21,8 +21,8 @@ mozilla::Atomic<bool> WriteStumbleOnThread::sIsUploading(false);
 mozilla::Atomic<bool> WriteStumbleOnThread::sIsAlreadyRunning(false);
 WriteStumbleOnThread::UploadFreqGuard WriteStumbleOnThread::sUploadFreqGuard = {0};
 
-#define FILENAME_INPROGRESS NS_LITERAL_CSTRING("stumbles.json")
-#define FILENAME_COMPLETED NS_LITERAL_CSTRING("stumbles.done.json")
+#define FILENAME_INPROGRESS NS_LITERAL_CSTRING("stumbles.json.gz")
+#define FILENAME_COMPLETED NS_LITERAL_CSTRING("stumbles.done.json.gz")
 #define OUTPUT_DIR NS_LITERAL_CSTRING("mozstumbler")
 
 class DeleteRunnable : public nsRunnable
@@ -64,15 +64,6 @@ WriteStumbleOnThread::UploadEnded(bool deleteUploadFile)
   target->Dispatch(event, NS_DISPATCH_NORMAL);
 }
 
-#define DUMP(o, s) \
-  do { \
-    const char* s2 = (s); \
-    uint32_t dummy; \
-    nsresult rv = (o)->Write((s2), strlen(s2), &dummy); \
-    if (NS_WARN_IF(NS_FAILED(rv))) \
-    STUMBLER_ERR("write err"); \
-  } while (0)
-
 void
 WriteStumbleOnThread::WriteJSON(Partition aPart)
 {
@@ -87,10 +78,10 @@ WriteStumbleOnThread::WriteJSON(Partition aPart)
     return;
   }
 
-  nsCOMPtr<nsIFileOutputStream> ostream = do_CreateInstance("@mozilla.org/network/file-output-stream;1");
-  rv = ostream->Init(tmpFile, PR_WRONLY | PR_APPEND, 0666, 0);
+  nsRefPtr<nsGZFileWriter> gzWriter = new nsGZFileWriter(nsGZFileWriter::Append);
+  rv = gzWriter->Init(tmpFile);
   if (NS_WARN_IF(NS_FAILED(rv))) {
-    STUMBLER_ERR("Open a file for stumble failed");
+    STUMBLER_ERR("gzWriter init failed");
     return;
   }
 
@@ -105,8 +96,8 @@ WriteStumbleOnThread::WriteJSON(Partition aPart)
 
   // Need to add "]}" after the last item
   if (aPart == Partition::End) {
-    DUMP(ostream, "]}");
-    rv = ostream->Close();
+    gzWriter->Write("]}");
+    rv = gzWriter->Finish();
     if (NS_WARN_IF(NS_FAILED(rv))) {
       STUMBLER_ERR("ostream finish failed");
     }
@@ -136,14 +127,14 @@ WriteStumbleOnThread::WriteJSON(Partition aPart)
 
   // Need to add "{items:[" before the first item
   if (aPart == Partition::Begining) {
-    DUMP(ostream, "{\"items\":[{");
+    gzWriter->Write("{\"items\":[{");
   } else if (aPart == Partition::Middle) {
-    DUMP(ostream, ",{");
+    gzWriter->Write(",{");
   }
-  DUMP(ostream, mDesc.get());
+  gzWriter->Write(mDesc.get());
   //  one item is ended with '}' (e.g. {item})
-  DUMP(ostream, "}");
-  rv = ostream->Close();
+  gzWriter->Write("}");
+  rv = gzWriter->Finish();
   if (NS_WARN_IF(NS_FAILED(rv))) {
     STUMBLER_ERR("ostream finish failed");
   }
@@ -297,21 +288,12 @@ WriteStumbleOnThread::Upload()
 
   // prepare json into nsIInputStream
   nsCOMPtr<nsIInputStream> inStream;
-  rv = NS_NewLocalFileInputStream(getter_AddRefs(inStream), tmpFile, -1, -1,
-                                  nsIFileInputStream::DEFER_OPEN);
+  rv = NS_NewLocalFileInputStream(getter_AddRefs(inStream), tmpFile);
   if (NS_FAILED(rv)) {
     sIsUploading = false;
     return;
   }
 
-  nsCString bufStr;
-  rv = NS_ReadInputStreamToString(inStream, bufStr, fileSize);
-
-  if (NS_FAILED(rv)) {
-    sIsUploading = false;
-    return;
-  }
-
-  nsRefPtr<nsIRunnable> uploader = new UploadStumbleRunnable(bufStr);
+  nsRefPtr<nsIRunnable> uploader = new UploadStumbleRunnable(inStream);
   NS_DispatchToMainThread(uploader);
 }