diff --git a/dom/base/nsFormData.cpp b/dom/base/nsFormData.cpp
index b1fd0d85551..da486d2cc2d 100644
--- a/dom/base/nsFormData.cpp
+++ b/dom/base/nsFormData.cpp
@@ -6,9 +6,7 @@
 #include "nsIVariant.h"
 #include "nsIInputStream.h"
 #include "mozilla/dom/File.h"
-#include "mozilla/dom/File.h"
 #include "mozilla/dom/HTMLFormElement.h"
-#include "mozilla/dom/FormDataBinding.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -86,6 +84,119 @@ nsFormData::Append(const nsAString& aName, File& aBlob,
   AddNameFilePair(aName, &aBlob, filename);
 }
 
+void
+nsFormData::Delete(const nsAString& aName)
+{
+  // We have to use this slightly awkward for loop since uint32_t >= 0 is an
+  // error for being always true.
+  for (uint32_t i = mFormData.Length(); i-- > 0; ) {
+    if (aName.Equals(mFormData[i].name)) {
+      mFormData.RemoveElementAt(i);
+    }
+  }
+}
+
+void
+nsFormData::ExtractValue(const FormDataTuple& aTuple,
+                         OwningFileOrUSVString* aOutValue)
+{
+  if (aTuple.valueIsFile) {
+    aOutValue->SetAsFile() = aTuple.fileValue;
+  } else {
+    aOutValue->SetAsUSVString() = aTuple.stringValue;
+  }
+}
+
+void
+nsFormData::Get(const nsAString& aName,
+                Nullable<OwningFileOrUSVString>& aOutValue)
+{
+  for (uint32_t i = 0; i < mFormData.Length(); ++i) {
+    if (aName.Equals(mFormData[i].name)) {
+      ExtractValue(mFormData[i], &aOutValue.SetValue());
+      return;
+    }
+  }
+
+  aOutValue.SetNull();
+}
+
+void
+nsFormData::GetAll(const nsAString& aName,
+                   nsTArray<OwningFileOrUSVString>& aValues)
+{
+  for (uint32_t i = 0; i < mFormData.Length(); ++i) {
+    if (aName.Equals(mFormData[i].name)) {
+      OwningFileOrUSVString* element = aValues.AppendElement();
+      ExtractValue(mFormData[i], element);
+    }
+  }
+}
+
+bool
+nsFormData::Has(const nsAString& aName)
+{
+  for (uint32_t i = 0; i < mFormData.Length(); ++i) {
+    if (aName.Equals(mFormData[i].name)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+nsFormData::FormDataTuple*
+nsFormData::RemoveAllOthersAndGetFirstFormDataTuple(const nsAString& aName)
+{
+  FormDataTuple* lastFoundTuple = nullptr;
+  uint32_t lastFoundIndex = mFormData.Length();
+  // We have to use this slightly awkward for loop since uint32_t >= 0 is an
+  // error for being always true.
+  for (uint32_t i = mFormData.Length(); i-- > 0; ) {
+    if (aName.Equals(mFormData[i].name)) {
+      if (lastFoundTuple) {
+        // The one we found earlier was not the first one, we can remove it.
+        mFormData.RemoveElementAt(lastFoundIndex);
+      }
+
+      lastFoundTuple = &mFormData[i];
+      lastFoundIndex = i;
+    }
+  }
+
+  return lastFoundTuple;
+}
+
+void
+nsFormData::Set(const nsAString& aName, File& aBlob,
+                const Optional<nsAString>& aFilename)
+{
+  FormDataTuple* tuple = RemoveAllOthersAndGetFirstFormDataTuple(aName);
+  if (tuple) {
+    nsAutoString filename;
+    if (aFilename.WasPassed()) {
+      filename = aFilename.Value();
+    } else {
+      filename.SetIsVoid(true);
+    }
+
+    SetNameFilePair(tuple, aName, &aBlob, filename);
+  } else {
+    Append(aName, aBlob, aFilename);
+  }
+}
+
+void
+nsFormData::Set(const nsAString& aName, const nsAString& aValue)
+{
+  FormDataTuple* tuple = RemoveAllOthersAndGetFirstFormDataTuple(aName);
+  if (tuple) {
+    SetNameValuePair(tuple, aName, aValue);
+  } else {
+    Append(aName, aValue);
+  }
+}
+
 // -------------------------------------------------------------------------
 // nsIDOMFormData
 
diff --git a/dom/base/nsFormData.h b/dom/base/nsFormData.h
index 64e6c4ee719..97021cfc795 100644
--- a/dom/base/nsFormData.h
+++ b/dom/base/nsFormData.h
@@ -13,6 +13,7 @@
 #include "nsTArray.h"
 #include "mozilla/ErrorResult.h"
 #include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/FormDataBinding.h"
 
 namespace mozilla {
 class ErrorResult;
@@ -29,8 +30,48 @@ class nsFormData MOZ_FINAL : public nsIDOMFormData,
                              public nsFormSubmission,
                              public nsWrapperCache
 {
+private:
   ~nsFormData() {}
 
+  typedef mozilla::dom::File File;
+  struct FormDataTuple
+  {
+    nsString name;
+    nsString stringValue;
+    nsRefPtr<File> fileValue;
+    nsString filename;
+    bool valueIsFile;
+  };
+
+  // Returns the FormDataTuple to modify. This may be null, in which case
+  // no element with aName was found.
+  FormDataTuple*
+  RemoveAllOthersAndGetFirstFormDataTuple(const nsAString& aName);
+
+  void SetNameValuePair(FormDataTuple* aData,
+                        const nsAString& aName,
+                        const nsAString& aValue)
+  {
+    MOZ_ASSERT(aData);
+    aData->name = aName;
+    aData->stringValue = aValue;
+    aData->valueIsFile = false;
+  }
+
+  void SetNameFilePair(FormDataTuple* aData,
+                       const nsAString& aName,
+                       File* aBlob,
+                       const nsAString& aFilename)
+  {
+    MOZ_ASSERT(aData);
+    aData->name = aName;
+    aData->fileValue = aBlob;
+    aData->filename = aFilename;
+    aData->valueIsFile = true;
+  }
+
+  void ExtractValue(const FormDataTuple& aTuple,
+                    mozilla::dom::OwningFileOrUSVString* aOutValue);
 public:
   explicit nsFormData(nsISupports* aOwner = nullptr);
 
@@ -55,8 +96,15 @@ public:
               const mozilla::dom::Optional<mozilla::dom::NonNull<mozilla::dom::HTMLFormElement> >& aFormElement,
               mozilla::ErrorResult& aRv);
   void Append(const nsAString& aName, const nsAString& aValue);
-  void Append(const nsAString& aName, mozilla::dom::File& aBlob,
+  void Append(const nsAString& aName, File& aBlob,
               const mozilla::dom::Optional<nsAString>& aFilename);
+  void Delete(const nsAString& aName);
+  void Get(const nsAString& aName, mozilla::dom::Nullable<mozilla::dom::OwningFileOrUSVString>& aOutValue);
+  void GetAll(const nsAString& aName, nsTArray<mozilla::dom::OwningFileOrUSVString>& aValues);
+  bool Has(const nsAString& aName);
+  void Set(const nsAString& aName, File& aBlob,
+           const mozilla::dom::Optional<nsAString>& aFilename);
+  void Set(const nsAString& aName, const nsAString& aValue);
 
   // nsFormSubmission
   virtual nsresult GetEncodedSubmission(nsIURI* aURI,
@@ -65,35 +113,20 @@ public:
                                     const nsAString& aValue) MOZ_OVERRIDE
   {
     FormDataTuple* data = mFormData.AppendElement();
-    data->name = aName;
-    data->stringValue = aValue;
-    data->valueIsFile = false;
+    SetNameValuePair(data, aName, aValue);
     return NS_OK;
   }
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob,
+                                   File* aBlob,
                                    const nsString& aFilename) MOZ_OVERRIDE
   {
     FormDataTuple* data = mFormData.AppendElement();
-    data->name = aName;
-    data->fileValue = aBlob;
-    data->filename = aFilename;
-    data->valueIsFile = true;
+    SetNameFilePair(data, aName, aBlob, aFilename);
     return NS_OK;
   }
-
 private:
   nsCOMPtr<nsISupports> mOwner;
 
-  struct FormDataTuple
-  {
-    nsString name;
-    nsString stringValue;
-    nsCOMPtr<nsIDOMBlob> fileValue;
-    nsString filename;
-    bool valueIsFile;
-  };
-
   nsTArray<FormDataTuple> mFormData;
 };
 
diff --git a/dom/html/nsFormSubmission.cpp b/dom/html/nsFormSubmission.cpp
index 24336b7fcf4..984b7d8d395 100644
--- a/dom/html/nsFormSubmission.cpp
+++ b/dom/html/nsFormSubmission.cpp
@@ -38,6 +38,7 @@
 #include "nsContentUtils.h"
 
 #include "mozilla/dom/EncodingUtils.h"
+#include "mozilla/dom/File.h"
 
 using namespace mozilla;
 using mozilla::dom::EncodingUtils;
@@ -78,7 +79,7 @@ public:
   virtual nsresult AddNameValuePair(const nsAString& aName,
                                     const nsAString& aValue);
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob,
+                                   File* aBlob,
                                    const nsString& aFilename);
   virtual nsresult GetEncodedSubmission(nsIURI* aURI,
                                         nsIInputStream** aPostDataStream);
@@ -165,7 +166,7 @@ nsFSURLEncoded::AddIsindex(const nsAString& aValue)
 
 nsresult
 nsFSURLEncoded::AddNameFilePair(const nsAString& aName,
-                                nsIDOMBlob* aBlob,
+                                File* aBlob,
                                 const nsString& aFilename)
 {
   if (!mWarnedFileControl) {
@@ -174,9 +175,8 @@ nsFSURLEncoded::AddNameFilePair(const nsAString& aName,
   }
 
   nsAutoString filename;
-  nsCOMPtr<nsIDOMFile> file = do_QueryInterface(aBlob);
-  if (file) {
-    file->GetName(filename);
+  if (aBlob && aBlob->IsFile()) {
+    aBlob->GetName(filename);
   }
 
   return AddNameValuePair(aName, filename);
@@ -441,7 +441,7 @@ nsFSMultipartFormData::AddNameValuePair(const nsAString& aName,
 
 nsresult
 nsFSMultipartFormData::AddNameFilePair(const nsAString& aName,
-                                       nsIDOMBlob* aBlob,
+                                       File* aBlob,
                                        const nsString& aFilename)
 {
   // Encode the control name
@@ -459,9 +459,8 @@ nsFSMultipartFormData::AddNameFilePair(const nsAString& aName,
     } else {
       // Get and encode the filename
       nsAutoString filename16;
-      nsCOMPtr<nsIDOMFile> file = do_QueryInterface(aBlob);
-      if (file) {
-        rv = file->GetName(filename16);
+      if (aBlob->IsFile()) {
+        rv = aBlob->GetName(filename16);
         NS_ENSURE_SUCCESS(rv, rv);
       }
 
@@ -469,7 +468,7 @@ nsFSMultipartFormData::AddNameFilePair(const nsAString& aName,
         filename16.AssignLiteral("blob");
       } else {
         nsAutoString filepath16;
-        rv = file->GetPath(filepath16);
+        rv = aBlob->GetPath(filepath16);
         NS_ENSURE_SUCCESS(rv, rv);
         if (!filepath16.IsEmpty()) {
           // File.path includes trailing "/"
@@ -598,7 +597,7 @@ public:
   virtual nsresult AddNameValuePair(const nsAString& aName,
                                     const nsAString& aValue);
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob,
+                                   File* aBlob,
                                    const nsString& aFilename);
   virtual nsresult GetEncodedSubmission(nsIURI* aURI,
                                         nsIInputStream** aPostDataStream);
@@ -622,13 +621,12 @@ nsFSTextPlain::AddNameValuePair(const nsAString& aName,
 
 nsresult
 nsFSTextPlain::AddNameFilePair(const nsAString& aName,
-                               nsIDOMBlob* aBlob,
+                               File* aBlob,
                                const nsString& aFilename)
 {
   nsAutoString filename;
-  nsCOMPtr<nsIDOMFile> file = do_QueryInterface(aBlob);
-  if (file) {
-    file->GetName(filename);
+  if (aBlob && aBlob->IsFile()) {
+    aBlob->GetName(filename);
   }
 
   AddNameValuePair(aName, filename);
diff --git a/dom/html/nsFormSubmission.h b/dom/html/nsFormSubmission.h
index 27802f0fb94..d7b5e0d329c 100644
--- a/dom/html/nsFormSubmission.h
+++ b/dom/html/nsFormSubmission.h
@@ -20,7 +20,12 @@ class nsIDocShell;
 class nsIRequest;
 class nsISaveAsCharset;
 class nsIMultiplexInputStream;
-class nsIDOMBlob;
+
+namespace mozilla {
+namespace dom {
+class File;
+} // namespace dom
+} // namespace mozilla
 
 /**
  * Class for form submissions; encompasses the function to call to submit as
@@ -51,9 +56,9 @@ public:
    * @param aFilename the filename to be used (not void)
    */
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob,
+                                   mozilla::dom::File* aBlob,
                                    const nsString& aFilename) = 0;
-  
+
   /**
    * Reports whether the instance supports AddIsindex().
    *
@@ -161,7 +166,7 @@ public:
   virtual nsresult AddNameValuePair(const nsAString& aName,
                                     const nsAString& aValue) MOZ_OVERRIDE;
   virtual nsresult AddNameFilePair(const nsAString& aName,
-                                   nsIDOMBlob* aBlob,
+                                   mozilla::dom::File* aBlob,
                                    const nsString& aFilename) MOZ_OVERRIDE;
   virtual nsresult GetEncodedSubmission(nsIURI* aURI,
                                         nsIInputStream** aPostDataStream) MOZ_OVERRIDE;
diff --git a/dom/html/test/test_formData.html b/dom/html/test/test_formData.html
index 9248debd9e4..f39c940b0a5 100644
--- a/dom/html/test/test_formData.html
+++ b/dom/html/test/test_formData.html
@@ -14,7 +14,90 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=690659
 <script type="text/javascript">
 SimpleTest.waitForExplicitFinish();
 
-function runTest() {
+function testHas() {
+  var f = new FormData();
+  f.append("foo", "bar");
+  f.append("another", "value");
+  ok(f.has("foo"), "has() on existing name should be true.");
+  ok(f.has("another"), "has() on existing name should be true.");
+  ok(!f.has("nonexistent"), "has() on non-existent name should be false.");
+}
+
+function testGet() {
+  var f = new FormData();
+  f.append("foo", "bar");
+  f.append("foo", "bar2");
+  f.append("blob", new Blob(["hey"], { type: 'text/plain' }));
+  f.append("file", new File(["hey"], 'testname',  {type: 'text/plain'}));
+
+  is(f.get("foo"), "bar", "get() on existing name should return first value");
+  ok(f.get("blob") instanceof Blob, "get() on existing name should return first value");
+  is(f.get("blob").type, 'text/plain', "get() on existing name should return first value");
+  ok(f.get("file") instanceof File, "get() on existing name should return first value");
+  is(f.get("file").name, 'testname', "get() on existing name should return first value");
+
+  is(f.get("nonexistent"), null, "get() on non-existent name should return null.");
+}
+
+function testGetAll() {
+  var f = new FormData();
+  f.append("other", "value");
+  f.append("foo", "bar");
+  f.append("foo", "bar2");
+  f.append("foo", new Blob(["hey"], { type: 'text/plain' }));
+
+  var arr = f.getAll("foo");
+  is(arr.length, 3, "getAll() should retrieve all matching entries.");
+  is(arr[0], "bar", "values should match and be in order");
+  is(arr[1], "bar2", "values should match and be in order");
+  ok(arr[2] instanceof Blob, "values should match and be in order");
+
+  is(f.get("nonexistent"), null, "get() on non-existent name should return null.");
+}
+
+function testDelete() {
+  var f = new FormData();
+  f.append("other", "value");
+  f.append("foo", "bar");
+  f.append("foo", "bar2");
+  f.append("foo", new Blob(["hey"], { type: 'text/plain' }));
+
+  ok(f.has("foo"), "has() on existing name should be true.");
+  f.delete("foo");
+  ok(!f.has("foo"), "has() on deleted name should be false.");
+  is(f.getAll("foo").length, 0, "all entries should be deleted.");
+
+  is(f.getAll("other").length, 1, "other names should still be there.");
+  f.delete("other");
+  is(f.getAll("other").length, 0, "all entries should be deleted.");
+}
+
+function testSet() {
+  var f = new FormData();
+
+  f.set("other", "value");
+  ok(f.has("other"), "set() on new name should be similar to append()");
+  is(f.getAll("other").length, 1, "set() on new name should be similar to append()");
+
+  f.append("other", "value2");
+  is(f.getAll("other").length, 2, "append() should not replace existing entries.");
+
+  f.append("foo", "bar");
+  f.append("other", "value3");
+  f.append("other", "value3");
+  f.append("other", "value3");
+  is(f.getAll("other").length, 5, "append() should not replace existing entries.");
+
+  f.set("other", "value4");
+  is(f.getAll("other").length, 1, "set() should replace existing entries.");
+  is(f.getAll("other")[0], "value4", "set() should replace existing entries.");
+}
+
+function testIterate() {
+  todo(false, "Implement this in Bug 1085284.");
+}
+
+function testSend() {
     var xhr = new XMLHttpRequest();
     xhr.open("POST", "form_submit_server.sjs");
     xhr.onload = function () {
@@ -62,6 +145,17 @@ function runTest() {
     xhr.send(fd);
 }
 
+function runTest() {
+  testHas();
+  testGet();
+  testGetAll();
+  testDelete();
+  testSet();
+  testIterate();
+  // Finally, send an XHR and verify the response matches.
+  testSend();
+}
+
 runTest()
 </script>
 </body>
diff --git a/dom/webidl/FormData.webidl b/dom/webidl/FormData.webidl
index 4e4bef26850..1003cc06688 100644
--- a/dom/webidl/FormData.webidl
+++ b/dom/webidl/FormData.webidl
@@ -7,8 +7,17 @@
  * http://xhr.spec.whatwg.org
  */
 
+typedef (File or USVString) FormDataEntryValue;
+
 [Constructor(optional HTMLFormElement form)]
 interface FormData {
-  void append(DOMString name, Blob value, optional DOMString filename);
-  void append(DOMString name, DOMString value);
+  void append(USVString name, Blob value, optional USVString filename);
+  void append(USVString name, USVString value);
+  void delete(USVString name);
+  FormDataEntryValue? get(USVString name);
+  sequence<FormDataEntryValue> getAll(USVString name);
+  boolean has(USVString name);
+  void set(USVString name, Blob value, optional USVString filename);
+  void set(USVString name, USVString value);
+  // iterable<USVString, FormDataEntryValue>; - Bug 1127703
 };