diff --git a/mozjs/src/gc/collections.rs b/mozjs/src/gc/collections.rs
index 28dd76867f..9b942281b6 100644
--- a/mozjs/src/gc/collections.rs
+++ b/mozjs/src/gc/collections.rs
@@ -5,6 +5,7 @@ use mozjs_sys::jsapi::JS;
 use mozjs_sys::jsgc::GCMethods;
 use mozjs_sys::jsval::JSVal;
 use mozjs_sys::trace::Traceable;
+use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 
 /// A vector of items to be rooted with `RootedVec`.
@@ -157,3 +158,219 @@ impl<T: Traceable + 'static> Drop for RootedTraceableBox<T> {
         }
     }
 }
+
+/// Inline, fixed capacity buffer of JS values with GC barriers.
+/// Backed by `[Heap<JSVal>; N]`, and a manual `len`.
+pub struct FixedValueArray<const N: usize> {
+    elems: [Heap<JSVal>; N],
+    len: usize,
+}
+
+unsafe impl<const N: usize> Traceable for FixedValueArray<N> {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        for i in 0..self.len {
+            self.elems[i].trace(trc);
+        }
+    }
+}
+
+impl<const N: usize> FixedValueArray<N> {
+    /// Create a new empty array, with all slots initialized to Undefined.
+    pub fn new() -> Self {
+        Self {
+            elems: std::array::from_fn(|_| Heap::<JSVal>::default()),
+            len: 0,
+        }
+    }
+
+    /// Current logical length.
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Max capacity (const generic).
+    pub fn capacity(&self) -> usize {
+        N
+    }
+
+    /// Push a JSVal into the next slot.
+    /// Panics if you exceed capacity N.
+    pub fn push(&mut self, v: JSVal) {
+        assert!(self.len < N, "FixedValueArray capacity ({}) exceeded", N);
+        self.elems[self.len].set(v);
+        self.len += 1;
+    }
+
+    /// Return a stable HandleValueArray that SpiderMonkey can consume.
+    pub fn as_handle_value_array(&self) -> JS::HandleValueArray {
+        JS::HandleValueArray {
+            length_: self.len,
+            elements_: self.elems.as_ptr() as *const JSVal,
+        }
+    }
+}
+
+/// A rooted wrapper for a FixedValueArray<N>.
+pub struct RootedFixedValueArray<'a, const N: usize> {
+    ptr: *mut FixedValueArray<N>,
+    _phantom: PhantomData<&'a mut FixedValueArray<N>>,
+}
+
+impl<'a, const N: usize> RootedFixedValueArray<'a, N> {
+    /// Allocate a FixedValueArray<N>, register it in RootedTraceableSet so the GC
+    pub fn new() -> Self {
+        let boxed = Box::new(FixedValueArray::<N>::new());
+        let raw = Box::into_raw(boxed);
+
+        unsafe {
+            RootedTraceableSet::add(raw);
+        }
+
+        RootedFixedValueArray {
+            ptr: raw,
+            _phantom: PhantomData,
+        }
+    }
+
+    /// Push a JSVal into the underlying fixed array.
+    pub fn push(&mut self, v: JSVal) {
+        unsafe { (&mut *self.ptr).push(v) }
+    }
+
+    /// Produce a stable HandleValueArray view into the initialized prefix.
+    pub fn as_handle_value_array(&self) -> JS::HandleValueArray {
+        unsafe { (&*self.ptr).as_handle_value_array() }
+    }
+
+    pub fn len(&self) -> usize {
+        unsafe { (&*self.ptr).len() }
+    }
+
+    pub fn capacity(&self) -> usize {
+        unsafe { (&*self.ptr).capacity() }
+    }
+}
+
+impl<'a, const N: usize> Drop for RootedFixedValueArray<'a, N> {
+    fn drop(&mut self) {
+        unsafe {
+            RootedTraceableSet::remove(self.ptr);
+            let _ = Box::from_raw(self.ptr);
+        }
+    }
+}
+
+/// A growable, rooted, GC traceable collection of JS values.
+/// Elements are stored in boxed Heap<JSVal> cells so each GC cell has a stable
+/// address even if the Vec reallocates.
+pub struct DynamicValueArray {
+    elems: Vec<Box<Heap<JSVal>>>,
+}
+
+unsafe impl Traceable for DynamicValueArray {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        for heap_box in &self.elems {
+            heap_box.trace(trc);
+        }
+    }
+}
+
+impl DynamicValueArray {
+    pub fn new() -> Self {
+        DynamicValueArray { elems: Vec::new() }
+    }
+
+    pub fn with_capacity(cap: usize) -> Self {
+        DynamicValueArray {
+            elems: Vec::with_capacity(cap),
+        }
+    }
+
+    pub fn push(&mut self, v: JSVal) {
+        let cell = Heap::boxed(v);
+        self.elems.push(cell);
+    }
+
+    pub fn len(&self) -> usize {
+        self.elems.len()
+    }
+}
+
+/// A rooted, wrapper for DynamicValueArray which also owns
+/// Vec<JSVal> used to present a HandleValueArray view to SpiderMonkey.
+pub struct RootedDynamicValueArray {
+    ptr: *mut DynamicValueArray,
+    scratch: Vec<JSVal>,
+}
+
+unsafe impl Traceable for RootedDynamicValueArray {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        (&*self.ptr).trace(trc)
+    }
+}
+
+impl RootedDynamicValueArray {
+    pub fn new() -> Self {
+        let boxed = Box::new(DynamicValueArray::new());
+        let raw = Box::into_raw(boxed);
+
+        unsafe {
+            RootedTraceableSet::add(raw);
+        }
+
+        RootedDynamicValueArray {
+            ptr: raw,
+            scratch: Vec::new(),
+        }
+    }
+
+    pub fn with_capacity(cap: usize) -> Self {
+        let boxed = Box::new(DynamicValueArray::with_capacity(cap));
+        let raw = Box::into_raw(boxed);
+
+        unsafe {
+            RootedTraceableSet::add(raw);
+        }
+
+        RootedDynamicValueArray {
+            ptr: raw,
+            scratch: Vec::with_capacity(cap),
+        }
+    }
+
+    pub fn push(&mut self, v: JSVal) {
+        unsafe {
+            (&mut *self.ptr).push(v);
+        }
+    }
+
+    fn rebuild_scratch(&mut self) {
+        let inner = unsafe { &*self.ptr };
+        self.scratch.clear();
+        self.scratch.reserve(inner.len());
+        for heap_box in &inner.elems {
+            self.scratch.push(heap_box.get());
+        }
+    }
+
+    pub fn as_handle_value_array(&mut self) -> JS::HandleValueArray {
+        self.rebuild_scratch();
+        JS::HandleValueArray {
+            length_: self.scratch.len(),
+            elements_: self.scratch.as_ptr(),
+        }
+    }
+
+    pub fn len(&self) -> usize {
+        unsafe { (&*self.ptr).len() }
+    }
+}
+
+impl Drop for RootedDynamicValueArray {
+    fn drop(&mut self) {
+        unsafe {
+            RootedTraceableSet::remove(self.ptr);
+            let _ = Box::from_raw(self.ptr);
+        }
+    }
+}
diff --git a/mozjs/src/gc/macros.rs b/mozjs/src/gc/macros.rs
index 0fd70c9270..fc575d1ccd 100644
--- a/mozjs/src/gc/macros.rs
+++ b/mozjs/src/gc/macros.rs
@@ -47,3 +47,23 @@ macro_rules! auto_root {
         let $($var)+: $crate::rust::CustomAutoRootedGuard<$type> = __root.root($cx);
     };
 }
+
+#[macro_export]
+macro_rules! rooted_fixed_array {
+    (let mut $name:ident : $cap:expr) => {
+        let mut $name = $crate::gc::RootedFixedValueArray::<'_, { $cap }>::new();
+    };
+    (let $name:ident : $cap:expr) => {
+        let $name = $crate::gc::RootedFixedValueArray::<'_, { $cap }>::new();
+    };
+}
+
+#[macro_export]
+macro_rules! rooted_dynamic_array {
+    (let mut $name:ident) => {
+        let mut $name = $crate::gc::RootedDynamicValueArray::new();
+    };
+    (let mut $name:ident : $cap:expr) => {
+        let mut $name = $crate::gc::RootedDynamicValueArray::with_capacity($cap);
+    };
+}