diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 2d188d411040..e4448ff834c2 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -19,6 +19,7 @@
     IDLBuiltinType,
     IDLNullValue,
     IDLNullableType,
+    IDLObject,
     IDLType,
     IDLInterfaceMember,
     IDLUndefinedValue,
@@ -1090,6 +1091,12 @@ def wrapObjectTemplate(templateBody, nullValue, isDefinitelyObject, type,
         typeName = "%s::%s" % (CGDictionary.makeModuleName(type.inner),
                                CGDictionary.makeDictionaryName(type.inner))
         declType = CGGeneric(typeName)
+        empty = "%s::empty(cx)" % typeName
+
+        if isMember != "Dictionary" and type_needs_tracing(type):
+            declType = CGTemplatedType("RootedTraceableBox", declType)
+            empty = "RootedTraceableBox::new(%s)" % empty
+
         template = ("match FromJSValConvertible::from_jsval(cx, ${val}, ()) {\n"
                     "    Ok(ConversionResult::Success(dictionary)) => dictionary,\n"
                     "    Ok(ConversionResult::Failure(error)) => {\n"
@@ -1098,7 +1105,7 @@ def wrapObjectTemplate(templateBody, nullValue, isDefinitelyObject, type,
                     "    _ => { %s },\n"
                     "}" % (indent(failOrPropagate, 8), exceptionCode))
 
-        return handleOptional(template, declType, handleDefaultNull("%s::empty(cx)" % typeName))
+        return handleOptional(template, declType, handleDefaultNull(empty))
 
     if type.isVoid():
         # This one only happens for return values, and its easy: Just
@@ -3147,7 +3154,7 @@ def __init__(self, errorResult, arguments, argsPre, returnType,
         args = CGList([CGGeneric(arg) for arg in argsPre], ", ")
         for (a, name) in arguments:
             # XXXjdm Perhaps we should pass all nontrivial types by borrowed pointer
-            if a.type.isDictionary():
+            if a.type.isDictionary() and not type_needs_tracing(a.type):
                 name = "&" + name
             args.append(CGGeneric(name))
 
@@ -5577,6 +5584,7 @@ def generate_imports(config, cgthings, descriptors, callbacks=None, dictionaries
         'dom::bindings::utils::trace_global',
         'dom::bindings::trace::JSTraceable',
         'dom::bindings::trace::RootedTraceable',
+        'dom::bindings::trace::RootedTraceableBox',
         'dom::bindings::callback::CallSetup',
         'dom::bindings::callback::CallbackContainer',
         'dom::bindings::callback::CallbackInterface',
@@ -6163,6 +6171,45 @@ def define(self):
         return stripTrailingWhitespace(self.root.define())
 
 
+def type_needs_tracing(t):
+    assert isinstance(t, IDLObject), (t, type(t))
+
+    if t.isType():
+        if isinstance(t, IDLWrapperType):
+            return type_needs_tracing(t.inner)
+
+        if t.nullable():
+            return type_needs_tracing(t.inner)
+
+        if t.isAny():
+            return True
+
+        if t.isObject():
+            return True
+
+        if t.isSequence():
+            return type_needs_tracing(t.inner)
+
+        return False
+
+    if t.isDictionary():
+        if t.parent and type_needs_tracing(t.parent):
+            return True
+
+        if any(type_needs_tracing(member.type) for member in t.members):
+            return True
+
+        return False
+
+    if t.isInterface():
+        return False
+
+    if t.isEnum():
+        return False
+
+    assert False, (t, type(t))
+
+
 def argument_type(descriptorProvider, ty, optional=False, defaultValue=None, variadic=False):
     info = getJSToNativeConversionInfo(
         ty, descriptorProvider, isArgument=True)
@@ -6176,7 +6223,7 @@ def argument_type(descriptorProvider, ty, optional=False, defaultValue=None, var
     elif optional and not defaultValue:
         declType = CGWrapper(declType, pre="Option<", post=">")
 
-    if ty.isDictionary():
+    if ty.isDictionary() and not type_needs_tracing(ty):
         declType = CGWrapper(declType, pre="&")
 
     return declType.define()
diff --git a/components/script/dom/customevent.rs b/components/script/dom/customevent.rs
index 942253c30dca..f11f2643dad5 100644
--- a/components/script/dom/customevent.rs
+++ b/components/script/dom/customevent.rs
@@ -10,6 +10,7 @@ use dom::bindings::inheritance::Castable;
 use dom::bindings::js::{MutHeapJSVal, Root};
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::event::Event;
 use dom::globalscope::GlobalScope;
 use js::jsapi::{HandleValue, JSContext};
@@ -51,7 +52,7 @@ impl CustomEvent {
     #[allow(unsafe_code)]
     pub fn Constructor(global: &GlobalScope,
                        type_: DOMString,
-                       init: &CustomEventBinding::CustomEventInit)
+                       init: RootedTraceableBox<CustomEventBinding::CustomEventInit>)
                        -> Fallible<Root<CustomEvent>> {
         Ok(CustomEvent::new(global,
                             Atom::from(type_),
diff --git a/components/script/dom/errorevent.rs b/components/script/dom/errorevent.rs
index a89a7b7e5274..37197b6125a9 100644
--- a/components/script/dom/errorevent.rs
+++ b/components/script/dom/errorevent.rs
@@ -11,6 +11,7 @@ use dom::bindings::inheritance::Castable;
 use dom::bindings::js::{MutHeapJSVal, Root};
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::event::{Event, EventBubbles, EventCancelable};
 use dom::globalscope::GlobalScope;
 use js::jsapi::{HandleValue, JSContext};
@@ -72,7 +73,8 @@ impl ErrorEvent {
 
     pub fn Constructor(global: &GlobalScope,
                        type_: DOMString,
-                       init: &ErrorEventBinding::ErrorEventInit) -> Fallible<Root<ErrorEvent>>{
+                       init: RootedTraceableBox<ErrorEventBinding::ErrorEventInit>)
+                       -> Fallible<Root<ErrorEvent>>{
         let msg = match init.message.as_ref() {
             Some(message) => message.clone(),
             None => DOMString::new(),
@@ -91,9 +93,6 @@ impl ErrorEvent {
 
         let cancelable = EventCancelable::from(init.parent.cancelable);
 
-        // Dictionaries need to be rooted
-        // https://github.com/servo/servo/issues/6381
-        rooted!(in(global.get_cx()) let error = init.error.get());
         let event = ErrorEvent::new(
                 global,
                 Atom::from(type_),
@@ -103,7 +102,7 @@ impl ErrorEvent {
                 file_name,
                 line_num,
                 col_num,
-                error.handle());
+                init.error.handle());
         Ok(event)
     }
 
diff --git a/components/script/dom/extendablemessageevent.rs b/components/script/dom/extendablemessageevent.rs
index b070007f8318..dd0360cb408d 100644
--- a/components/script/dom/extendablemessageevent.rs
+++ b/components/script/dom/extendablemessageevent.rs
@@ -9,6 +9,7 @@ use dom::bindings::inheritance::Castable;
 use dom::bindings::js::Root;
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::event::Event;
 use dom::eventtarget::EventTarget;
 use dom::extendableevent::ExtendableEvent;
@@ -47,15 +48,14 @@ impl ExtendableMessageEvent {
 
     pub fn Constructor(worker: &ServiceWorkerGlobalScope,
                        type_: DOMString,
-                       init: &ExtendableMessageEventBinding::ExtendableMessageEventInit)
+                       init: RootedTraceableBox<ExtendableMessageEventBinding::ExtendableMessageEventInit>)
                        -> Fallible<Root<ExtendableMessageEvent>> {
         let global = worker.upcast::<GlobalScope>();
-        rooted!(in(global.get_cx()) let data = init.data.get());
         let ev = ExtendableMessageEvent::new(global,
                                              Atom::from(type_),
                                              init.parent.parent.bubbles,
                                              init.parent.parent.cancelable,
-                                             data.handle(),
+                                             init.data.handle(),
                                              init.origin.clone().unwrap(),
                                              init.lastEventId.clone().unwrap());
         Ok(ev)
diff --git a/components/script/dom/messageevent.rs b/components/script/dom/messageevent.rs
index b066cf810fe2..3df960d0882e 100644
--- a/components/script/dom/messageevent.rs
+++ b/components/script/dom/messageevent.rs
@@ -10,6 +10,7 @@ use dom::bindings::inheritance::Castable;
 use dom::bindings::js::Root;
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::event::Event;
 use dom::eventtarget::EventTarget;
 use dom::globalscope::GlobalScope;
@@ -60,16 +61,13 @@ impl MessageEvent {
 
     pub fn Constructor(global: &GlobalScope,
                        type_: DOMString,
-                       init: &MessageEventBinding::MessageEventInit)
+                       init: RootedTraceableBox<MessageEventBinding::MessageEventInit>)
                        -> Fallible<Root<MessageEvent>> {
-        // Dictionaries need to be rooted
-        // https://github.com/servo/servo/issues/6381
-        rooted!(in(global.get_cx()) let data = init.data.get());
         let ev = MessageEvent::new(global,
                                    Atom::from(type_),
                                    init.parent.bubbles,
                                    init.parent.cancelable,
-                                   data.handle(),
+                                   init.data.handle(),
                                    init.origin.clone(),
                                    init.lastEventId.clone());
         Ok(ev)
diff --git a/components/script/dom/popstateevent.rs b/components/script/dom/popstateevent.rs
index 7db2eea8fe66..1282d847d7c6 100644
--- a/components/script/dom/popstateevent.rs
+++ b/components/script/dom/popstateevent.rs
@@ -10,6 +10,7 @@ use dom::bindings::inheritance::Castable;
 use dom::bindings::js::{MutHeapJSVal, Root};
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::event::Event;
 use dom::window::Window;
 use js::jsapi::{HandleValue, JSContext};
@@ -55,7 +56,7 @@ impl PopStateEvent {
 
     pub fn Constructor(window: &Window,
                        type_: DOMString,
-                       init: &PopStateEventBinding::PopStateEventInit)
+                       init: RootedTraceableBox<PopStateEventBinding::PopStateEventInit>)
                        -> Fallible<Root<PopStateEvent>> {
         Ok(PopStateEvent::new(window,
                               Atom::from(type_),
diff --git a/components/script/dom/request.rs b/components/script/dom/request.rs
index bf4914f82550..a81d9f767b6f 100644
--- a/components/script/dom/request.rs
+++ b/components/script/dom/request.rs
@@ -20,6 +20,7 @@ use dom::bindings::error::{Error, Fallible};
 use dom::bindings::js::{MutNullableJS, Root};
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::str::{ByteString, DOMString, USVString};
+use dom::bindings::trace::RootedTraceableBox;
 use dom::globalscope::GlobalScope;
 use dom::headers::{Guard, Headers};
 use dom::promise::Promise;
@@ -80,7 +81,7 @@ impl Request {
     // https://fetch.spec.whatwg.org/#dom-request
     pub fn Constructor(global: &GlobalScope,
                        input: RequestInfo,
-                       init: &RequestInit)
+                       init: RootedTraceableBox<RequestInit>)
                        -> Fallible<Root<Request>> {
         // Step 1
         let temporary_request: NetTraitsRequest;
@@ -311,7 +312,7 @@ impl Request {
         if let Some(possible_header) = init.headers.as_ref() {
             match possible_header {
                 &HeadersInit::Headers(ref init_headers) => {
-                    headers_copy = init_headers.clone();
+                    headers_copy = Root::from_ref(&*init_headers);
                 }
                 &HeadersInit::ByteStringSequenceSequence(ref init_sequence) => {
                     try!(headers_copy.fill(Some(
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 677d5c611db9..1582647ca335 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -27,6 +27,7 @@ use dom::bindings::num::Finite;
 use dom::bindings::refcounted::TrustedPromise;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::str::{ByteString, DOMString, USVString};
+use dom::bindings::trace::RootedTraceableBox;
 use dom::bindings::weakref::MutableWeakRef;
 use dom::blob::{Blob, BlobImpl};
 use dom::globalscope::GlobalScope;
@@ -402,7 +403,7 @@ impl TestBindingMethods for TestBinding {
         }
     }
 
-    fn DictMatchesPassedValues(&self, arg: &TestDictionary) -> bool {
+    fn DictMatchesPassedValues(&self, arg: RootedTraceableBox<TestDictionary>) -> bool {
         arg.type_.as_ref().map(|s| s == "success").unwrap_or(false) &&
             arg.nonRequiredNullable.is_none() &&
             arg.nonRequiredNullable2 == Some(None)
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index b68bd492fd08..d1eba0245e0c 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -26,6 +26,7 @@ use dom::bindings::refcounted::Trusted;
 use dom::bindings::reflector::DomObject;
 use dom::bindings::str::DOMString;
 use dom::bindings::structuredclone::StructuredCloneData;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::bindings::utils::{GlobalStaticData, WindowProxyHandler};
 use dom::bluetooth::BluetoothExtraPermissionData;
 use dom::browsingcontext::BrowsingContext;
@@ -921,7 +922,7 @@ impl WindowMethods for Window {
 
     #[allow(unrooted_must_root)]
     // https://fetch.spec.whatwg.org/#fetch-method
-    fn Fetch(&self, input: RequestOrUSVString, init: &RequestInit) -> Rc<Promise> {
+    fn Fetch(&self, input: RequestOrUSVString, init: RootedTraceableBox<RequestInit>) -> Rc<Promise> {
         fetch::Fetch(&self.upcast(), input, init)
     }
 
diff --git a/components/script/dom/workerglobalscope.rs b/components/script/dom/workerglobalscope.rs
index 16bd699da7c1..03e531c5f16f 100644
--- a/components/script/dom/workerglobalscope.rs
+++ b/components/script/dom/workerglobalscope.rs
@@ -14,6 +14,7 @@ use dom::bindings::js::{MutNullableJS, Root};
 use dom::bindings::reflector::DomObject;
 use dom::bindings::settings_stack::AutoEntryScript;
 use dom::bindings::str::DOMString;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::crypto::Crypto;
 use dom::dedicatedworkerglobalscope::DedicatedWorkerGlobalScope;
 use dom::globalscope::GlobalScope;
@@ -314,7 +315,7 @@ impl WorkerGlobalScopeMethods for WorkerGlobalScope {
 
     #[allow(unrooted_must_root)]
     // https://fetch.spec.whatwg.org/#fetch-method
-    fn Fetch(&self, input: RequestOrUSVString, init: &RequestInit) -> Rc<Promise> {
+    fn Fetch(&self, input: RequestOrUSVString, init: RootedTraceableBox<RequestInit>) -> Rc<Promise> {
         fetch::Fetch(self.upcast(), input, init)
     }
 }
diff --git a/components/script/fetch.rs b/components/script/fetch.rs
index f1fd49147b7a..0e7cacdfc1a0 100644
--- a/components/script/fetch.rs
+++ b/components/script/fetch.rs
@@ -10,6 +10,7 @@ use dom::bindings::error::Error;
 use dom::bindings::js::Root;
 use dom::bindings::refcounted::{Trusted, TrustedPromise};
 use dom::bindings::reflector::DomObject;
+use dom::bindings::trace::RootedTraceableBox;
 use dom::globalscope::GlobalScope;
 use dom::headers::Guard;
 use dom::promise::Promise;
@@ -68,7 +69,7 @@ fn request_init_from_request(request: NetTraitsRequest) -> NetTraitsRequestInit
 
 // https://fetch.spec.whatwg.org/#fetch-method
 #[allow(unrooted_must_root)]
-pub fn Fetch(global: &GlobalScope, input: RequestInfo, init: &RequestInit) -> Rc<Promise> {
+pub fn Fetch(global: &GlobalScope, input: RequestInfo, init: RootedTraceableBox<RequestInit>) -> Rc<Promise> {
     let core_resource_thread = global.core_resource_thread();
 
     // Step 1