diff --git a/mfbt/decimal/Decimal.cpp b/mfbt/decimal/Decimal.cpp
--- a/mfbt/decimal/Decimal.cpp
+++ b/mfbt/decimal/Decimal.cpp
@@ -23,22 +23,20 @@
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "platform/Decimal.h"
+#include "Decimal.h"
+#include "moz-decimal-utils.h"
 
-#include "wtf/Allocator.h"
-#include "wtf/MathExtras.h"
-#include "wtf/Noncopyable.h"
-#include "wtf/text/StringBuilder.h"
+using namespace moz_decimal_utils;
 
 #include <algorithm>
 #include <float.h>
 
 namespace blink {
 
 namespace DecimalPrivate {
 
@@ -690,17 +688,17 @@ Decimal Decimal::floor() const
     if (isNegative() && !isMultiplePowersOfTen(m_data.coefficient(), numberOfDropDigits))
         ++result;
     return Decimal(sign(), 0, result);
 }
 
 Decimal Decimal::fromDouble(double doubleValue)
 {
     if (std::isfinite(doubleValue))
-        return fromString(String::numberToStringECMAScript(doubleValue));
+        return fromString(mozToString(doubleValue));
 
     if (std::isinf(doubleValue))
         return infinity(doubleValue < 0 ? Negative : Positive);
 
     return nan();
 }
 
 Decimal Decimal::fromString(const String& str)
@@ -931,17 +929,17 @@ Decimal Decimal::round() const
     result /= 10;
     return Decimal(sign(), 0, result);
 }
 
 double Decimal::toDouble() const
 {
     if (isFinite()) {
         bool valid;
-        const double doubleValue = toString().toDouble(&valid);
+        const double doubleValue = mozToDouble(toString(), &valid);
         return valid ? doubleValue : std::numeric_limits<double>::quiet_NaN();
     }
 
     if (isInfinity())
         return isNegative() ? -std::numeric_limits<double>::infinity() : std::numeric_limits<double>::infinity();
 
     return std::numeric_limits<double>::quiet_NaN();
 }
@@ -984,17 +982,17 @@ String Decimal::toString() const
             ++coefficient;
 
         while (originalExponent < 0 && coefficient && !(coefficient % 10)) {
             coefficient /= 10;
             ++originalExponent;
         }
     }
 
-    const String digits = String::number(coefficient);
+    const String digits = mozToString(coefficient);
     int coefficientLength = static_cast<int>(digits.length());
     const int adjustedExponent = originalExponent + coefficientLength - 1;
     if (originalExponent <= 0 && adjustedExponent >= -6) {
         if (!originalExponent) {
             builder.append(digits);
             return builder.toString();
         }
 
@@ -1026,14 +1024,27 @@ String Decimal::toString() const
         if (adjustedExponent) {
             builder.append(adjustedExponent < 0 ? "e" : "e+");
             builder.appendNumber(adjustedExponent);
         }
     }
     return builder.toString();
 }
 
+bool Decimal::toString(char* strBuf, size_t bufLength) const
+{
+  ASSERT(bufLength > 0);
+  String str = toString();
+  size_t length = str.copy(strBuf, bufLength);
+  if (length < bufLength) {
+    strBuf[length] = '\0';
+    return true;
+  }
+  strBuf[bufLength - 1] = '\0';
+  return false;
+}
+
 Decimal Decimal::zero(Sign sign)
 {
     return Decimal(EncodedData(sign, EncodedData::ClassZero));
 }
 
 } // namespace blink
diff --git a/mfbt/decimal/Decimal.h b/mfbt/decimal/Decimal.h
--- a/mfbt/decimal/Decimal.h
+++ b/mfbt/decimal/Decimal.h
@@ -23,26 +23,49 @@
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+/**
+ * Imported from:
+ * https://chromium.googlesource.com/chromium/src.git/+/master/third_party/WebKit/Source/platform/Decimal.h
+ * Check UPSTREAM-GIT-SHA for the commit ID of the last update from Blink core.
+ */
+
 #ifndef Decimal_h
 #define Decimal_h
 
+#include "mozilla/Assertions.h"
+#include <stdint.h>
 #include "mozilla/Types.h"
 
-#include "platform/PlatformExport.h"
-#include "wtf/Allocator.h"
-#include "wtf/Assertions.h"
-#include "wtf/text/WTFString.h"
-#include <stdint.h>
+#include <string>
+
+#ifndef ASSERT
+#define DEFINED_ASSERT_FOR_DECIMAL_H 1
+#define ASSERT MOZ_ASSERT
+#endif
+
+#define PLATFORM_EXPORT
+
+// To use USING_FAST_MALLOC we'd need:
+// https://chromium.googlesource.com/chromium/src.git/+/master/third_party/WebKit/Source/wtf/Allocator.h
+// Since we don't allocate Decimal objects, no need.
+#define USING_FAST_MALLOC(type) \
+  void ignore_this_dummy_method() = delete
+
+#define DISALLOW_NEW()                                          \
+    private:                                                    \
+        void* operator new(size_t) = delete;                    \
+        void* operator new(size_t, void*) = delete;             \
+    public:
 
 namespace blink {
 
 namespace DecimalPrivate {
 class SpecialValueHandler;
 }
 
 // This class represents decimal base floating point number.
@@ -139,27 +162,28 @@ public:
     MFBT_API Decimal abs() const;
     MFBT_API Decimal ceil() const;
     MFBT_API Decimal floor() const;
     MFBT_API Decimal remainder(const Decimal&) const;
     MFBT_API Decimal round() const;
 
     MFBT_API double toDouble() const;
     // Note: toString method supports infinity and nan but fromString not.
-    MFBT_API String toString() const;
+    MFBT_API std::string toString() const;
+    MFBT_API bool toString(char* strBuf, size_t bufLength) const;
 
     static MFBT_API Decimal fromDouble(double);
     // fromString supports following syntax EBNF:
     //  number ::= sign? digit+ ('.' digit*) (exponent-marker sign? digit+)?
     //          | sign? '.' digit+ (exponent-marker sign? digit+)?
     //  sign ::= '+' | '-'
     //  exponent-marker ::= 'e' | 'E'
     //  digit ::= '0' | '1' | ... | '9'
     // Note: fromString doesn't support "infinity" and "nan".
-    static MFBT_API Decimal fromString(const String&);
+    static MFBT_API Decimal fromString(const std::string& aValue);
     static MFBT_API Decimal infinity(Sign);
     static MFBT_API Decimal nan();
     static MFBT_API Decimal zero(Sign);
 
     // You should not use below methods. We expose them for unit testing.
     MFBT_API explicit Decimal(const EncodedData&);
     const EncodedData& value() const { return m_data; }
 
@@ -178,9 +202,20 @@ private:
 
     Sign sign() const { return m_data.sign(); }
 
     EncodedData m_data;
 };
 
 } // namespace blink
 
+namespace mozilla {
+typedef blink::Decimal Decimal;
+} // namespace mozilla
+
+#undef USING_FAST_MALLOC
+
+#ifdef DEFINED_ASSERT_FOR_DECIMAL_H
+#undef DEFINED_ASSERT_FOR_DECIMAL_H
+#undef ASSERT
+#endif
+
 #endif // Decimal_h
