diff --git a/content/html/content/test/forms/test_input_number_data.js b/content/html/content/test/forms/test_input_number_data.js
index e17f452fee19..2fa6cf2d2bac 100644
--- a/content/html/content/test/forms/test_input_number_data.js
+++ b/content/html/content/test/forms/test_input_number_data.js
@@ -16,15 +16,6 @@ var tests = [
     langTag: "de", inputWithGrouping: "123.456,78",
     inputWithoutGrouping: "123456,78", value: 123456.78
   },
-  // Extra german test to check that a locale that uses '.' as its grouping
-  // separator doesn't result in it being invalid (due to step mismatch) due
-  // to the de-localization code mishandling numbers that look like other
-  // numbers formatted for English speakers (i.e. treating this as 123.456
-  // instead of 123456):
-  { desc: "German (test 2)",
-    langTag: "de", inputWithGrouping: "123.456",
-    inputWithoutGrouping: "123456", value: 123456
-  },
   { desc: "Hebrew",
     langTag: "he", inputWithGrouping: "123,456.78",
     inputWithoutGrouping: "123456.78", value: 123456.78
diff --git a/layout/forms/nsNumberControlFrame.cpp b/layout/forms/nsNumberControlFrame.cpp
index 66505a16b8ef..8813c5bea5b5 100644
--- a/layout/forms/nsNumberControlFrame.cpp
+++ b/layout/forms/nsNumberControlFrame.cpp
@@ -627,52 +627,23 @@ nsNumberControlFrame::GetValueOfAnonTextControl(nsAString& aValue)
   HTMLInputElement::FromContent(mTextField)->GetValue(aValue);
 
 #ifdef ENABLE_INTL_API
-  // Here we need to de-localize any number typed in by the user. That is, we
-  // need to convert it from the number format of the user's language, region,
-  // etc. to the format that the HTML 5 spec defines to be a "valid
-  // floating-point number":
+  // Here we check if the text field's value is a localized serialization of a
+  // number. If it is we set aValue to the de-localize value, but only if the
+  // localized value isn't also a valid floating-point number according to the
+  // HTML 5 spec:
   //
   //   http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#floating-point-numbers
   //
-  // so that it can be parsed by functions like HTMLInputElement::
-  // StringToDecimal (the HTML-5-conforming parsing function) which don't know
-  // how to handle numbers that are formatted differently (for example, with
-  // non-ASCII digits, with grouping separator characters or with a decimal
-  // separator character other than '.').
-  //
-  // We need to be careful to avoid normalizing numbers that are already
-  // formatted for a locale that matches the format of HTML 5's "valid
-  // floating-point number" and have no grouping separator characters. (In
-  // other words we want to return the number as specified by the user, not the
-  // de-localized serialization, since the latter will normalize the value.)
-  // For example, if the user's locale is English and the user types in "2e2"
-  // then inputElement.value should be "2e2" and not "100". This is because
-  // content (and tests) expect us to avoid "normalizing" the number that the
-  // user types in if it's not necessary in order to make sure it conforms to
-  // HTML 5's "valid floating-point number" format.
-  //
-  // Note that we also need to be careful when trying to avoid normalization.
-  // For example, just because "1.234" _looks_ like a valid floating-point
-  // number according to the spec does not mean that it should be returned
-  // as-is. If the user's locale is German, then this represents the value
-  // 1234, not 1.234, so it still needs to be de-localized. Alternatively, if
-  // the user's locale is English and they type in "1,234" we _do_ need to
-  // normalize the number to "1234" because HTML 5's valid floating-point
-  // number format does not allow the ',' grouping separator. We can detect all
-  // the cases where we need to convert by seeing if the locale-specific
-  // parsing function understands the user input to mean the same thing as the
-  // HTML-5-conforming parsing function. If so, then we should return the value
-  // as-is to avoid normalization. Otherwise, we return the de-localized
-  // serialization.
+  // This is because content (and tests) expect us to avoid "normalizing" the
+  // number that the user types in if it's not necessary. (E.g. if the user
+  // types "2e2" then inputElement.value should be "2e2" and not "100".
   ICUUtils::LanguageTagIterForContent langTagIter(mContent);
   double value = ICUUtils::ParseNumber(aValue, langTagIter);
   if (NS_finite(value) &&
-      value != HTMLInputElement::StringToDecimal(aValue).toDouble()) {
+      !HTMLInputElement::StringToDecimal(aValue).isFinite()) {
     aValue.Truncate();
     aValue.AppendFloat(value);
   }
-  // else, we return whatever FromContent put into aValue (the number as typed
-  // in by the user)
 #endif
 }