diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index 271915f4fa8..7351cbfeac4 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -21,7 +21,6 @@ use gecko_bindings::bindings::RawServoRuleNode;
 use gecko_bindings::bindings::RawServoRuleNodeStrong;
 use gecko_bindings::bindings::RawServoSupportsRule;
 use gecko_bindings::bindings::ServoCssRules;
-use gecko_bindings::bindings::StyleUseCounters;
 use gecko_bindings::structs::RawServoAnimationValue;
 use gecko_bindings::structs::RawServoDeclarationBlock;
 use gecko_bindings::structs::RawServoFontFaceRule;
@@ -40,7 +39,6 @@ use stylesheets::{CounterStyleRule, CssRules, FontFaceRule, FontFeatureValuesRul
 use stylesheets::{DocumentRule, ImportRule, KeyframesRule, MediaRule, NamespaceRule, PageRule};
 use stylesheets::{StyleRule, StylesheetContents, SupportsRule};
 use stylesheets::keyframes_rule::Keyframe;
-use use_counters::UseCounters;
 
 macro_rules! impl_arc_ffi {
     ($servo_type:ty => $gecko_type:ty[$addref:ident, $release:ident]) => {
@@ -61,9 +59,6 @@ macro_rules! impl_arc_ffi {
     };
 }
 
-impl_arc_ffi!(UseCounters => StyleUseCounters
-              [Servo_UseCounters_AddRef, Servo_UseCounters_Release]);
-
 impl_arc_ffi!(Locked<CssRules> => ServoCssRules
               [Servo_CssRules_AddRef, Servo_CssRules_Release]);
 
diff --git a/components/style/gecko_bindings/sugar/ownership.rs b/components/style/gecko_bindings/sugar/ownership.rs
index 2bc85f53ff7..91c7a504eb1 100644
--- a/components/style/gecko_bindings/sugar/ownership.rs
+++ b/components/style/gecko_bindings/sugar/ownership.rs
@@ -305,6 +305,15 @@ pub struct OwnedOrNull<GeckoType> {
 }
 
 impl<GeckoType> OwnedOrNull<GeckoType> {
+    /// Returns a null pointer.
+    #[inline]
+    pub fn null() -> Self {
+        Self {
+            ptr: ptr::null_mut(),
+            _marker: PhantomData,
+        }
+    }
+
     /// Returns whether this pointer is null.
     #[inline]
     pub fn is_null(&self) -> bool {
diff --git a/components/style/use_counters/mod.rs b/components/style/use_counters/mod.rs
index 03fdc045365..92bc6adb01a 100644
--- a/components/style/use_counters/mod.rs
+++ b/components/style/use_counters/mod.rs
@@ -4,10 +4,10 @@
 
 //! Various stuff for CSS property use counters.
 
+#[cfg(feature = "gecko")]
+use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use properties::{NonCustomPropertyId, NON_CUSTOM_PROPERTY_ID_COUNT};
-// FIXME(emilio): We need AtomicU32 on stable ASAP...
-use std::sync::atomic::AtomicUsize;
-use std::sync::atomic::Ordering;
+use std::cell::Cell;
 
 #[cfg(target_pointer_width = "64")]
 const BITS_PER_ENTRY: usize = 64;
@@ -18,7 +18,7 @@ const BITS_PER_ENTRY: usize = 32;
 /// One bit per each non-custom CSS property.
 #[derive(Default)]
 pub struct NonCustomPropertyUseCounters {
-    storage: [AtomicUsize; (NON_CUSTOM_PROPERTY_ID_COUNT - 1 + BITS_PER_ENTRY) / BITS_PER_ENTRY],
+    storage: [Cell<usize>; (NON_CUSTOM_PROPERTY_ID_COUNT - 1 + BITS_PER_ENTRY) / BITS_PER_ENTRY],
 }
 
 impl NonCustomPropertyUseCounters {
@@ -36,7 +36,8 @@ impl NonCustomPropertyUseCounters {
     #[inline]
     pub fn record(&self, id: NonCustomPropertyId) {
         let (bucket, pattern) = Self::bucket_and_pattern(id);
-        self.storage[bucket].fetch_or(pattern, Ordering::Relaxed);
+        let bucket = &self.storage[bucket];
+        bucket.set(bucket.get() | pattern)
     }
 
     /// Returns whether a given non-custom property ID has been recorded
@@ -44,7 +45,15 @@ impl NonCustomPropertyUseCounters {
     #[inline]
     pub fn recorded(&self, id: NonCustomPropertyId) -> bool {
         let (bucket, pattern) = Self::bucket_and_pattern(id);
-        self.storage[bucket].load(Ordering::Relaxed) & pattern != 0
+        self.storage[bucket].get() & pattern != 0
+    }
+
+    /// Merge `other` into `self`.
+    #[inline]
+    fn merge(&self, other: &Self) {
+        for (bucket, other_bucket) in self.storage.iter().zip(other.storage.iter()) {
+            bucket.set(bucket.get() | other_bucket.get())
+        }
     }
 }
 
@@ -55,3 +64,24 @@ pub struct UseCounters {
     /// document's stylesheets.
     pub non_custom_properties: NonCustomPropertyUseCounters,
 }
+
+impl UseCounters {
+    /// Merge the use counters.
+    ///
+    /// Used for parallel parsing, where we parse off-main-thread.
+    #[inline]
+    pub fn merge(&self, other: &Self) {
+        self.non_custom_properties.merge(&other.non_custom_properties)
+    }
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasFFI for UseCounters {
+    type FFIType = ::gecko_bindings::structs::StyleUseCounters;
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasSimpleFFI for UseCounters {}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasBoxFFI for UseCounters {}