diff --git a/ports/geckolib/gecko_bindings/lib.rs b/ports/geckolib/gecko_bindings/lib.rs
index b6d684b5891..d1bfb30985d 100644
--- a/ports/geckolib/gecko_bindings/lib.rs
+++ b/ports/geckolib/gecko_bindings/lib.rs
@@ -2,9 +2,13 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#![feature(concat_idents)]
+#![feature(type_macros)]
+
 extern crate heapsize;
 
 #[allow(dead_code, non_camel_case_types)]
 pub mod bindings;
+pub mod ptr;
 #[allow(dead_code, non_camel_case_types, non_snake_case, non_upper_case_globals)]
 pub mod structs;
diff --git a/ports/geckolib/gecko_bindings/ptr.rs b/ports/geckolib/gecko_bindings/ptr.rs
new file mode 100644
index 00000000000..089df6f70b1
--- /dev/null
+++ b/ports/geckolib/gecko_bindings/ptr.rs
@@ -0,0 +1,59 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use bindings::*;
+use heapsize::HeapSizeOf;
+use std::fmt::{self, Debug};
+
+// Defines an Arc-like type that manages a refcounted Gecko object stored
+// in a ThreadSafeFooHolder smart pointer.  Used in tandem with the
+// NS_DECL_HOLDER_FFI_REFCOUNTING-defined types and functions in Gecko.
+macro_rules! define_holder_arc {
+    ($arc_type:ident, $name:ident, $holder_type:ident) => (
+        #[derive(PartialEq)]
+        pub struct $arc_type {
+            ptr: *mut $holder_type,
+        }
+
+        impl $arc_type {
+            pub fn new(data: *mut $holder_type) -> $arc_type {
+                debug_assert!(!data.is_null());
+                unsafe { concat_idents!(Gecko_AddRef, $name, ArbitraryThread)(data); }
+                $arc_type {
+                    ptr: data
+                }
+            }
+
+            pub fn as_raw(&self) -> *mut $holder_type { self.ptr }
+        }
+
+        unsafe impl Send for $arc_type {}
+        unsafe impl Sync for $arc_type {}
+
+        impl Clone for $arc_type {
+            fn clone(&self) -> $arc_type {
+                $arc_type::new(self.ptr)
+            }
+        }
+
+        impl Drop for $arc_type {
+            fn drop(&mut self) {
+                unsafe { concat_idents!(Gecko_Release, $name, ArbitraryThread)(self.ptr); }
+            }
+        }
+
+        impl HeapSizeOf for $arc_type {
+            fn heap_size_of_children(&self) -> usize { 0 }
+        }
+
+        impl Debug for $arc_type {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(f, stringify!($name))
+            }
+        }
+    )
+}
+
+define_holder_arc!(GeckoArcPrincipal, Principal, ThreadSafePrincipalHolder);
+define_holder_arc!(GeckoArcURI, URI, ThreadSafeURIHolder);