diff --git a/xpcom/ds/nsSupportsPrimitives.cpp b/xpcom/ds/nsSupportsPrimitives.cpp
index 76c1fb44414..a3901a44c5d 100644
--- a/xpcom/ds/nsSupportsPrimitives.cpp
+++ b/xpcom/ds/nsSupportsPrimitives.cpp
@@ -6,8 +6,24 @@
 
 #include "nsSupportsPrimitives.h"
 #include "nsMemory.h"
+#include "mozilla/Assertions.h"
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/Snprintf.h"
+#include <algorithm>
+
+template<typename T>
+static char*
+DataToString(const char* aFormat, T aData)
+{
+  static const int size = 32;
+  char buf[size];
+
+  int len = snprintf_literal(buf, aFormat, aData);
+  MOZ_ASSERT(len >= 0);
+
+  return static_cast<char*>(nsMemory::Clone(buf, std::min(len + 1, size) *
+                                                 sizeof(char)));
+}
 
 /***************************************************************************/
 
@@ -23,7 +39,6 @@ nsSupportsIDImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_ID;
-
   return NS_OK;
 }
 
@@ -31,11 +46,13 @@ NS_IMETHODIMP
 nsSupportsIDImpl::GetData(nsID** aData)
 {
   NS_ASSERTION(aData, "Bad pointer");
+
   if (mData) {
-    *aData = (nsID*)nsMemory::Clone(mData, sizeof(nsID));
-    return *aData ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+    *aData = static_cast<nsID*>(nsMemory::Clone(mData, sizeof(nsID)));
+  } else {
+    *aData = nullptr;
   }
-  *aData = nullptr;
+
   return NS_OK;
 }
 
@@ -45,28 +62,29 @@ nsSupportsIDImpl::SetData(const nsID* aData)
   if (mData) {
     free(mData);
   }
+
   if (aData) {
-    mData = (nsID*)nsMemory::Clone(aData, sizeof(nsID));
+    mData = static_cast<nsID*>(nsMemory::Clone(aData, sizeof(nsID)));
   } else {
     mData = nullptr;
   }
+
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsSupportsIDImpl::ToString(char** aResult)
 {
-  char* result;
   NS_ASSERTION(aResult, "Bad pointer");
+
   if (mData) {
-    result = mData->ToString();
+    *aResult = mData->ToString();
   } else {
     static const char nullStr[] = "null";
-    result = (char*)nsMemory::Clone(nullStr, sizeof(nullStr));
+    *aResult = static_cast<char*>(nsMemory::Clone(nullStr, sizeof(nullStr)));
   }
 
-  *aResult = result;
-  return result ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  return NS_OK;
 }
 
 /*****************************************************************************
@@ -80,7 +98,6 @@ NS_IMETHODIMP
 nsSupportsCStringImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
-
   *aType = TYPE_CSTRING;
   return NS_OK;
 }
@@ -96,7 +113,6 @@ NS_IMETHODIMP
 nsSupportsCStringImpl::ToString(char** aResult)
 {
   *aResult = ToNewCString(mData);
-
   if (!*aResult) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -111,6 +127,7 @@ nsSupportsCStringImpl::SetData(const nsACString& aData)
   if (!ok) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
+
   return NS_OK;
 }
 
@@ -125,7 +142,6 @@ NS_IMETHODIMP
 nsSupportsStringImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
-
   *aType = TYPE_STRING;
   return NS_OK;
 }
@@ -141,7 +157,6 @@ NS_IMETHODIMP
 nsSupportsStringImpl::ToString(char16_t** aResult)
 {
   *aResult = ToNewUnicode(mData);
-
   if (!*aResult) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -156,6 +171,7 @@ nsSupportsStringImpl::SetData(const nsAString& aData)
   if (!ok) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
+
   return NS_OK;
 }
 
@@ -174,7 +190,6 @@ nsSupportsPRBoolImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRBOOL;
-
   return NS_OK;
 }
 
@@ -198,8 +213,9 @@ nsSupportsPRBoolImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
   const char* str = mData ? "true" : "false";
-  *aResult = (char*)nsMemory::Clone(str, (strlen(str) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = static_cast<char*>(nsMemory::Clone(str, (strlen(str) + 1) *
+                                                     sizeof(char)));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -217,7 +233,6 @@ nsSupportsPRUint8Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRUINT8;
-
   return NS_OK;
 }
 
@@ -240,11 +255,8 @@ NS_IMETHODIMP
 nsSupportsPRUint8Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[8];
-  snprintf_literal(buf, "%u", (unsigned int)mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%u", static_cast<unsigned int>(mData));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -262,7 +274,6 @@ nsSupportsPRUint16Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRUINT16;
-
   return NS_OK;
 }
 
@@ -285,11 +296,8 @@ NS_IMETHODIMP
 nsSupportsPRUint16Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[8];
-  snprintf_literal(buf, "%u", (unsigned int)mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%u", static_cast<unsigned int>(mData));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -307,7 +315,6 @@ nsSupportsPRUint32Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRUINT32;
-
   return NS_OK;
 }
 
@@ -330,11 +337,8 @@ NS_IMETHODIMP
 nsSupportsPRUint32Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[16];
-  snprintf_literal(buf, "%u", mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%u", mData);
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -352,7 +356,6 @@ nsSupportsPRUint64Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRUINT64;
-
   return NS_OK;
 }
 
@@ -375,11 +378,8 @@ NS_IMETHODIMP
 nsSupportsPRUint64Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[32];
-  snprintf_literal(buf, "%llu", mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%llu", mData);
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -397,7 +397,6 @@ nsSupportsPRTimeImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRTIME;
-
   return NS_OK;
 }
 
@@ -420,11 +419,8 @@ NS_IMETHODIMP
 nsSupportsPRTimeImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[32];
-  snprintf_literal(buf, "%" PRIu64, mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%" PRIu64, mData);
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -442,7 +438,6 @@ nsSupportsCharImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_CHAR;
-
   return NS_OK;
 }
 
@@ -465,14 +460,11 @@ NS_IMETHODIMP
 nsSupportsCharImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
+  *aResult = static_cast<char*>(moz_xmalloc(2 * sizeof(char)));
+  *aResult[0] = mData;
+  *aResult[1] = '\0';
 
-  char* result = (char*)moz_xmalloc(2 * sizeof(char));
-  if (result) {
-    result[0] = mData;
-    result[1] = '\0';
-  }
-  *aResult = result;
-  return result ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -490,7 +482,6 @@ nsSupportsPRInt16Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRINT16;
-
   return NS_OK;
 }
 
@@ -513,11 +504,8 @@ NS_IMETHODIMP
 nsSupportsPRInt16Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[8];
-  snprintf_literal(buf, "%d", (int)mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%d", static_cast<int>(mData));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -535,7 +523,6 @@ nsSupportsPRInt32Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRINT32;
-
   return NS_OK;
 }
 
@@ -558,11 +545,8 @@ NS_IMETHODIMP
 nsSupportsPRInt32Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[16];
-  snprintf_literal(buf, "%d", mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%d", mData);
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -580,7 +564,6 @@ nsSupportsPRInt64Impl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_PRINT64;
-
   return NS_OK;
 }
 
@@ -603,11 +586,8 @@ NS_IMETHODIMP
 nsSupportsPRInt64Impl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[32];
-  snprintf_literal(buf, "%" PRId64, mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%" PRId64, mData);
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -625,7 +605,6 @@ nsSupportsFloatImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_FLOAT;
-
   return NS_OK;
 }
 
@@ -648,11 +627,8 @@ NS_IMETHODIMP
 nsSupportsFloatImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[32];
-  snprintf_literal(buf, "%f", (double)mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%f", static_cast<double>(mData));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -670,7 +646,6 @@ nsSupportsDoubleImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_DOUBLE;
-
   return NS_OK;
 }
 
@@ -693,11 +668,8 @@ NS_IMETHODIMP
 nsSupportsDoubleImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-  char buf[32];
-  snprintf_literal(buf, "%f", mData);
-
-  *aResult = (char*)nsMemory::Clone(buf, (strlen(buf) + 1) * sizeof(char));
-  return  *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = DataToString("%f", mData);
+  return  NS_OK;
 }
 
 /***************************************************************************/
@@ -716,7 +688,6 @@ nsSupportsVoidImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_VOID;
-
   return NS_OK;
 }
 
@@ -739,11 +710,9 @@ NS_IMETHODIMP
 nsSupportsVoidImpl::ToString(char** aResult)
 {
   NS_ASSERTION(aResult, "Bad pointer");
-
   static const char str[] = "[raw data]";
-  char* result = (char*)nsMemory::Clone(str, sizeof(str));
-  *aResult = result;
-  return  result ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = static_cast<char*>(nsMemory::Clone(str, sizeof(str)));
+  return NS_OK;
 }
 
 /***************************************************************************/
@@ -770,7 +739,6 @@ nsSupportsInterfacePointerImpl::GetType(uint16_t* aType)
 {
   NS_ASSERTION(aType, "Bad pointer");
   *aType = TYPE_INTERFACE_POINTER;
-
   return NS_OK;
 }
 
@@ -778,10 +746,8 @@ NS_IMETHODIMP
 nsSupportsInterfacePointerImpl::GetData(nsISupports** aData)
 {
   NS_ASSERTION(aData, "Bad pointer");
-
   *aData = mData;
   NS_IF_ADDREF(*aData);
-
   return NS_OK;
 }
 
@@ -789,7 +755,6 @@ NS_IMETHODIMP
 nsSupportsInterfacePointerImpl::SetData(nsISupports* aData)
 {
   mData = aData;
-
   return NS_OK;
 }
 
@@ -799,10 +764,11 @@ nsSupportsInterfacePointerImpl::GetDataIID(nsID** aIID)
   NS_ASSERTION(aIID, "Bad pointer");
 
   if (mIID) {
-    *aIID = (nsID*)nsMemory::Clone(mIID, sizeof(nsID));
-    return *aIID ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+    *aIID = static_cast<nsID*>(nsMemory::Clone(mIID, sizeof(nsID)));
+  } else {
+    *aIID = nullptr;
   }
-  *aIID = nullptr;
+
   return NS_OK;
 }
 
@@ -812,8 +778,9 @@ nsSupportsInterfacePointerImpl::SetDataIID(const nsID* aIID)
   if (mIID) {
     free(mIID);
   }
+
   if (aIID) {
-    mIID = (nsID*)nsMemory::Clone(aIID, sizeof(nsID));
+    mIID = static_cast<nsID*>(nsMemory::Clone(aIID, sizeof(nsID)));
   } else {
     mIID = nullptr;
   }
@@ -827,11 +794,10 @@ nsSupportsInterfacePointerImpl::ToString(char** aResult)
   NS_ASSERTION(aResult, "Bad pointer");
 
   static const char str[] = "[interface pointer]";
-
   // jband sez: think about asking nsIInterfaceInfoManager whether
   // the interface has a known human-readable name
-  *aResult = (char*)nsMemory::Clone(str, sizeof(str));
-  return  *aResult ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+  *aResult = static_cast<char*>(nsMemory::Clone(str, sizeof(str)));
+  return  NS_OK;
 }
 
 /***************************************************************************/