diff --git a/components/canvas_traits/webgl_channel/mpsc.rs b/components/canvas_traits/webgl_channel/mpsc.rs
index 40acb050861..8e34bda8e9b 100644
--- a/components/canvas_traits/webgl_channel/mpsc.rs
+++ b/components/canvas_traits/webgl_channel/mpsc.rs
@@ -5,7 +5,6 @@
 use serde::{Deserialize, Serialize};
 use serde::{Deserializer, Serializer};
 
-#[macro_use]
 macro_rules! unreachable_serializable {
     ($name:ident) => {
         impl<T> Serialize for $name<T> {
diff --git a/components/devtools/actors/browsing_context.rs b/components/devtools/actors/browsing_context.rs
index 5692fb167cd..e301abc98d7 100644
--- a/components/devtools/actors/browsing_context.rs
+++ b/components/devtools/actors/browsing_context.rs
@@ -125,14 +125,14 @@ pub(crate) struct BrowsingContextActor {
     pub title: RefCell<String>,
     pub url: RefCell<String>,
     pub console: String,
-    pub emulation: String,
-    pub inspector: String,
-    pub timeline: String,
-    pub profiler: String,
-    pub performance: String,
-    pub styleSheets: String,
+    pub _emulation: String,
+    pub _inspector: String,
+    pub _timeline: String,
+    pub _profiler: String,
+    pub _performance: String,
+    pub _styleSheets: String,
     pub thread: String,
-    pub tab: String,
+    pub _tab: String,
     pub streams: RefCell<HashMap<StreamId, TcpStream>>,
     pub browsing_context_id: BrowsingContextId,
     pub active_pipeline: Cell<PipelineId>,
@@ -288,13 +288,13 @@ impl BrowsingContextActor {
             title: RefCell::new(String::from(title)),
             url: RefCell::new(url.into_string()),
             console: console,
-            emulation: emulation.name(),
-            inspector: inspector.name(),
-            timeline: timeline.name(),
-            profiler: profiler.name(),
-            performance: performance.name(),
-            styleSheets: styleSheets.name(),
-            tab: tabdesc.name(),
+            _emulation: emulation.name(),
+            _inspector: inspector.name(),
+            _timeline: timeline.name(),
+            _profiler: profiler.name(),
+            _performance: performance.name(),
+            _styleSheets: styleSheets.name(),
+            _tab: tabdesc.name(),
             thread: thread.name(),
             streams: RefCell::new(HashMap::new()),
             browsing_context_id: id,
diff --git a/components/media/media_channel/mpsc.rs b/components/media/media_channel/mpsc.rs
index 7d6a396185a..8651258c65a 100644
--- a/components/media/media_channel/mpsc.rs
+++ b/components/media/media_channel/mpsc.rs
@@ -6,7 +6,6 @@ use serde::{Deserialize, Serialize};
 use serde::{Deserializer, Serializer};
 use std::sync::mpsc;
 
-#[macro_use]
 macro_rules! unreachable_serializable {
     ($name:ident) => {
         impl<T> Serialize for $name<T> {
diff --git a/components/net/http_cache.rs b/components/net/http_cache.rs
index 81109df2bda..a743a05cdde 100644
--- a/components/net/http_cache.rs
+++ b/components/net/http_cache.rs
@@ -230,8 +230,8 @@ fn get_response_expiry(response: &Response) -> Duration {
         let max_heuristic = Duration::hours(24) - age;
         let heuristic_freshness = if let Some(last_modified) =
             // If the response has a Last-Modified header field,
-        // caches are encouraged to use a heuristic expiration value
-        // that is no more than some fraction of the interval since that time.
+            // caches are encouraged to use a heuristic expiration value
+            // that is no more than some fraction of the interval since that time.
             response.headers.typed_get::<LastModified>()
         {
             let current = time::now().to_timespec();
diff --git a/components/script/lib.rs b/components/script/lib.rs
index 86935833157..2fcae084fb6 100644
--- a/components/script/lib.rs
+++ b/components/script/lib.rs
@@ -2,9 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-#![feature(assoc_char_funcs)]
-#![feature(const_fn)]
 #![feature(const_fn_fn_ptr_basics)]
+#![feature(const_fn_trait_bound)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![feature(plugin)]
diff --git a/components/script_plugins/lib.rs b/components/script_plugins/lib.rs
index 0a4f70c5c58..c1dc92abb09 100644
--- a/components/script_plugins/lib.rs
+++ b/components/script_plugins/lib.rs
@@ -405,7 +405,10 @@ fn match_def_path(cx: &LateContext, def_id: DefId, path: &[Symbol]) -> bool {
 fn in_derive_expn(span: Span) -> bool {
     matches!(
         span.ctxt().outer_expn_data().kind,
-        ExpnKind::Macro(MacroKind::Derive, _)
+        ExpnKind::Macro {
+            kind: MacroKind::Derive,
+            ..
+        }
     )
 }
 
diff --git a/rust-toolchain b/rust-toolchain
index 02c828fea2f..b2eff28fe03 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-nightly-2021-03-12
+nightly-2021-05-18