diff --git a/layout/reftests/forms/input/number/number-pseudo-elements-ref.html b/layout/reftests/forms/input/number/number-pseudo-elements-ref.html
new file mode 100644
index 00000000000..263aeff1f81
--- /dev/null
+++ b/layout/reftests/forms/input/number/number-pseudo-elements-ref.html
@@ -0,0 +1,6 @@
+
+
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+
diff --git a/layout/reftests/forms/input/number/number-pseudo-elements.html b/layout/reftests/forms/input/number/number-pseudo-elements.html
new file mode 100644
index 00000000000..33cf40fcf24
--- /dev/null
+++ b/layout/reftests/forms/input/number/number-pseudo-elements.html
@@ -0,0 +1,20 @@
+
+
+
+
+
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diff --git a/layout/reftests/forms/input/number/reftest.list b/layout/reftests/forms/input/number/reftest.list
index de618b34912..cfc448602d0 100644
--- a/layout/reftests/forms/input/number/reftest.list
+++ b/layout/reftests/forms/input/number/reftest.list
@@ -20,3 +20,6 @@ fuzzy-if(/^Windows\x20NT\x205\.1/.test(http.oscpu),64,4) fuzzy-if(cocoaWidget,63
# focus
fails-if(B2G) needs-focus == focus-handling.html focus-handling-ref.html # bug 940760
+# pseudo-elements not usable from content:
+== number-pseudo-elements.html number-pseudo-elements-ref.html
+
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 92227cd7ab5..931cb3632cf 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -3661,6 +3661,18 @@ CSSParserImpl::ParsePseudoSelector(int32_t& aDataMask,
nsCSSPseudoClasses::Type pseudoClassType =
nsCSSPseudoClasses::GetPseudoType(pseudo);
+ if (!mUnsafeRulesEnabled &&
+ (pseudoElementType == nsCSSPseudoElements::ePseudo_mozNumberWrapper ||
+ pseudoElementType == nsCSSPseudoElements::ePseudo_mozNumberText ||
+ pseudoElementType == nsCSSPseudoElements::ePseudo_mozNumberSpinBox ||
+ pseudoElementType == nsCSSPseudoElements::ePseudo_mozNumberSpinUp ||
+ pseudoElementType == nsCSSPseudoElements::ePseudo_mozNumberSpinDown)) {
+ // Hide these pseudo-elements from content until we standardize them.
+ REPORT_UNEXPECTED_TOKEN(PEPseudoSelUnknown);
+ UngetToken();
+ return eSelectorParsingStatus_Error;
+ }
+
// We currently allow :-moz-placeholder and ::-moz-placeholder. We have to
// be a bit stricter regarding the pseudo-element parsing rules.
if (pseudoElementType == nsCSSPseudoElements::ePseudo_mozPlaceholder &&