--- a/gfx/wr/webrender/src/scene_builder_thread.rs
+++ b/gfx/wr/webrender/src/scene_builder_thread.rs
@@ -139,17 +139,17 @@ pub enum SceneBuilderRequest {
     DeleteDocument(DocumentId),
     WakeUp,
     Flush(MsgSender<()>),
     ClearNamespace(IdNamespace),
     SetFrameBuilderConfig(FrameBuilderConfig),
     SimulateLongSceneBuild(u32),
     SimulateLongLowPrioritySceneBuild(u32),
     Stop,
-    ReportMemory(MemoryReport, MsgSender<MemoryReport>),
+    ReportMemory(Box<MemoryReport>, MsgSender<Box<MemoryReport>>),
     #[cfg(feature = "capture")]
     SaveScene(CaptureConfig),
     #[cfg(feature = "replay")]
     LoadScenes(Vec<LoadScene>),
     DocumentsForDebugger
 }
 
 // Message from scene builder to render backend.
@@ -357,17 +357,17 @@ impl SceneBuilderThread {
                 }
                 Ok(SceneBuilderRequest::Stop) => {
                     self.tx.send(SceneBuilderResult::Stopped).unwrap();
                     // We don't need to send a WakeUp to api_tx because we only
                     // get the Stop when the RenderBackend loop is exiting.
                     break;
                 }
                 Ok(SceneBuilderRequest::ReportMemory(mut report, tx)) => {
-                    report += self.report_memory();
+                    (*report) += self.report_memory();
                     tx.send(report).unwrap();
                 }
                 Ok(SceneBuilderRequest::SimulateLongSceneBuild(time_ms)) => {
                     self.simulate_slow_ms = time_ms
                 }
                 Ok(SceneBuilderRequest::SimulateLongLowPrioritySceneBuild(_)) => {}
                 Err(_) => {
                     break;

--- a/gfx/wr/webrender_api/src/api.rs
+++ b/gfx/wr/webrender_api/src/api.rs
@@ -1004,17 +1004,17 @@ pub enum ApiMsg {
     /// to forward gecko-specific messages to the render thread preserving the ordering
     /// within the other messages.
     ExternalEvent(ExternalEvent),
     /// Removes all resources associated with a namespace.
     ClearNamespace(IdNamespace),
     /// Flush from the caches anything that isn't necessary, to free some memory.
     MemoryPressure,
     /// Collects a memory report.
-    ReportMemory(MsgSender<MemoryReport>),
+    ReportMemory(MsgSender<Box<MemoryReport>>),
     /// Change debugging options.
     DebugCommand(DebugCommand),
     /// Wakes the render backend's event loop up. Needed when an event is communicated
     /// through another channel.
     WakeUp,
     /// See `RenderApi::wake_scene_builder`.
     WakeSceneBuilder,
     /// Block until a round-trip to the scene builder thread has completed. This
@@ -1533,17 +1533,17 @@ impl RenderApi {
     pub fn notify_memory_pressure(&self) {
         self.api_sender.send(ApiMsg::MemoryPressure).unwrap();
     }
 
     /// Synchronously requests memory report.
     pub fn report_memory(&self) -> MemoryReport {
         let (tx, rx) = channel::msg_channel().unwrap();
         self.api_sender.send(ApiMsg::ReportMemory(tx)).unwrap();
-        rx.recv().unwrap()
+        *rx.recv().unwrap()
     }
 
     /// Update debugging flags.
     pub fn set_debug_flags(&self, flags: DebugFlags) {
         let cmd = DebugCommand::SetFlags(flags);
         self.api_sender.send(ApiMsg::DebugCommand(cmd)).unwrap();
     }