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diff --git a/js/src/jit-test/tests/wasm/ref-types/externref-boxing.js b/js/src/jit-test/tests/wasm/ref-types/externref-boxing.js
new file mode 100644
index 0000000000..854f3e7815
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+++ b/js/src/jit-test/tests/wasm/ref-types/externref-boxing.js
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+// Moving a JS value through a wasm externref is a pair of boxing/unboxing
+// conversions that leaves the value unchanged.  There are many cases,
+// along these axes:
+//
+//  - global variables
+//  - tables
+//  - function parameters and returns
+//  - struct fields [for the gc feature], see externref-boxing-struct.js
+
+// Global variables can receive values via several mechanisms:
+//
+// - on initialization when created from JS
+// - on initialization when created in Wasm, from an imported global
+// - through the "value" property if the value is mutable
+// - through the global.set wasm instruction, ditto
+//
+// Their values can be obtained in several ways:
+//
+// - through the "value" property
+// - through the global.get wasm instruction
+// - read when other globals are initialized from them
+
+// Set via initialization and read via 'value'
+
+for (let v of WasmExternrefValues)
+{
+    let g = new WebAssembly.Global({value: "externref"}, v);
+    assertEq(g.value, v);
+}
+
+// Set via 'value' and read via 'value'
+
+for (let v of WasmExternrefValues)
+{
+    let g = new WebAssembly.Global({value: "externref", mutable: true});
+    g.value = v;
+    assertEq(g.value, v);
+}
+
+// Set via initialization, then read via global.get and returned
+
+for (let v of WasmExternrefValues)
+{
+    let g = new WebAssembly.Global({value: "externref"}, v);
+    let ins = wasmEvalText(
+        `(module
+           (import "m" "g" (global $glob externref))
+           (func (export "f") (result externref)
+             (global.get $glob)))`,
+        {m:{g}});
+    assertEq(ins.exports.f(), v);
+}
+
+// Set via global.set, then read via 'value'
+
+for (let v of WasmExternrefValues)
+{
+    let g = new WebAssembly.Global({value: "externref", mutable: true});
+    let ins = wasmEvalText(
+        `(module
+           (import "m" "g" (global $glob (mut externref)))
+           (func (export "f") (param $v externref)
+             (global.set $glob (local.get $v))))`,
+        {m:{g}});
+    ins.exports.f(v);
+    assertEq(g.value, v);
+}
+
+// Tables of externref can receive values via several mechanisms:
+//
+// - through WebAssembly.Table.prototype.set()
+// - through the table.set, table.copy, and table.grow instructions
+// - through table.fill
+// - through WebAssembly.Table.prototype.grow()
+//
+// Their values can be read in several ways:
+//
+// - through WebAssembly.Table.prototype.get()
+// - through the table.get and table.copy instructions
+//
+// (Note, tables are always initialized to null when created from JS)
+
+// .set() and .get()
+
+for (let v of WasmExternrefValues)
+{
+    let t = new WebAssembly.Table({element: "externref", initial: 10});
+    t.set(3, v);
+    assertEq(t.get(3), v);
+}
+
+// write with table.set, read with .get()
+
+for (let v of WasmExternrefValues)
+{
+    let t = new WebAssembly.Table({element: "externref", initial: 10});
+    let ins = wasmEvalText(
+        `(module
+           (import "m" "t" (table $t 10 externref))
+           (func (export "f") (param $v externref)
+             (table.set $t (i32.const 3) (local.get $v))))`,
+        {m:{t}});
+    ins.exports.f(v);
+    assertEq(t.get(3), v);
+}
+
+// write with .set(), read with table.get
+
+for (let v of WasmExternrefValues)
+{
+    let t = new WebAssembly.Table({element: "externref", initial: 10});
+    let ins = wasmEvalText(
+        `(module
+           (import "m" "t" (table $t 10 externref))
+           (func (export "f") (result externref)
+             (table.get $t (i32.const 3))))`,
+        {m:{t}});
+    t.set(3, v);
+    assertEq(ins.exports.f(), v);
+}
+
+// Imported JS functions can receive externref values as parameters and return
+// them.
+
+for (let v of WasmExternrefValues)
+{
+    let returner = function () { return v; };
+    let receiver = function (w) { assertEq(w, v); };
+    let ins = wasmEvalText(
+        `(module
+           (import "m" "returner" (func $returner (result externref)))
+           (import "m" "receiver" (func $receiver (param externref)))
+           (func (export "test_returner") (result externref)
+             (call $returner))
+           (func (export "test_receiver") (param $v externref)
+             (call $receiver (local.get $v))))`,
+        {m:{returner, receiver}});
+    assertEq(ins.exports.test_returner(), v);
+    ins.exports.test_receiver(v);
+}