diff --git a/Cargo.lock b/Cargo.lock
index 449ceba3875..a0a6ed54a51 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5329,9 +5329,9 @@ checksum = "c111b5bd5695e56cffe5129854aa230b39c93a305372fdbb2668ca2394eea9f8"
 
 [[package]]
 name = "smallbitvec"
-version = "2.3.0"
+version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1764fe2b30ee783bfe3b9b37b2649d8d590b3148bb12e0079715d4d5c673562e"
+checksum = "797a4eaffb90d896f29698d45676f9f940a71936d7574996a7df54593ba209fa"
 
 [[package]]
 name = "smallvec"
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index b9af35b8cac..157829412ce 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -3331,7 +3331,7 @@ impl Document {
     pub fn element_state_will_change(&self, el: &Element) {
         let mut entry = self.ensure_pending_restyle(el);
         if entry.snapshot.is_none() {
-            entry.snapshot = Some(Snapshot::new(el.html_element_in_html_document()));
+            entry.snapshot = Some(Snapshot::new());
         }
         let snapshot = entry.snapshot.as_mut().unwrap();
         if snapshot.state.is_none() {
@@ -3347,7 +3347,7 @@ impl Document {
         // could in theory do it in the DOM I think.
         let mut entry = self.ensure_pending_restyle(el);
         if entry.snapshot.is_none() {
-            entry.snapshot = Some(Snapshot::new(el.html_element_in_html_document()));
+            entry.snapshot = Some(Snapshot::new());
         }
         if attr.local_name() == &local_name!("style") {
             entry.hint.insert(RestyleHint::RESTYLE_STYLE_ATTRIBUTE);
@@ -3359,12 +3359,21 @@ impl Document {
 
         let snapshot = entry.snapshot.as_mut().unwrap();
         if attr.local_name() == &local_name!("id") {
+            if snapshot.id_changed {
+                return;
+            }
             snapshot.id_changed = true;
         } else if attr.local_name() == &local_name!("class") {
+            if snapshot.class_changed {
+                return;
+            }
             snapshot.class_changed = true;
         } else {
             snapshot.other_attributes_changed = true;
         }
+        if !snapshot.changed_attrs.contains(attr.local_name()) {
+            snapshot.changed_attrs.push(attr.local_name().clone());
+        }
         if snapshot.attrs.is_none() {
             let attrs = el
                 .attrs()
diff --git a/components/style/invalidation/element/invalidation_map.rs b/components/style/invalidation/element/invalidation_map.rs
index 59143dd0025..b822e47545e 100644
--- a/components/style/invalidation/element/invalidation_map.rs
+++ b/components/style/invalidation/element/invalidation_map.rs
@@ -196,7 +196,7 @@ pub struct InvalidationMap {
     /// A list of document state dependencies in the rules we represent.
     pub document_state_selectors: Vec<DocumentStateDependency>,
     /// A map of other attribute affecting selectors.
-    pub other_attribute_affecting_selectors: PrecomputedHashMap<Atom, SmallVec<[Dependency; 1]>>,
+    pub other_attribute_affecting_selectors: PrecomputedHashMap<LocalName, SmallVec<[Dependency; 1]>>,
 }
 
 impl InvalidationMap {
@@ -461,7 +461,6 @@ impl<'a> SelectorVisitor for SelectorDependencyCollector<'a> {
     }
 
     fn visit_simple_selector(&mut self, s: &Component<SelectorImpl>) -> bool {
-        #[cfg(feature = "gecko")]
         use crate::selector_parser::NonTSPseudoClass;
 
         match *s {
diff --git a/components/style/matching.rs b/components/style/matching.rs
index 677f024acfa..e8c6e55520f 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -7,7 +7,6 @@
 #![allow(unsafe_code)]
 #![deny(missing_docs)]
 
-use crate::animation::AnimationState;
 use crate::computed_value_flags::ComputedValueFlags;
 use crate::context::{ElementCascadeInputs, QuirksMode, SelectorFlagsMap};
 use crate::context::{SharedStyleContext, StyleContext};
@@ -438,6 +437,8 @@ trait PrivateMatchMethods: TElement {
         _restyle_hint: RestyleHint,
         _important_rules_changed: bool,
     ) {
+        use crate::animation::AnimationState;
+
         let this_opaque = self.as_node().opaque();
         let shared_context = context.shared;
         let mut animation_states = shared_context.animation_states.write();
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 863da15d65c..f0c9c7cad78 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -68,8 +68,7 @@ pub type AnimationValueMap = FxHashMap<LonghandId, AnimationValue>;
 ///
 /// FIXME: We need to add a path for custom properties, but that's trivial after
 /// this (is a similar path to that of PropertyDeclaration).
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
-#[derive(Debug)]
+#[derive(Debug, MallocSizeOf)]
 #[repr(u16)]
 pub enum AnimationValue {
     % for prop in data.longhands:
@@ -420,6 +419,7 @@ impl AnimationValue {
     ///
     /// SERVO ONLY: This doesn't properly handle things like updating 'em' units
     /// when animated font-size.
+    #[cfg(feature = "servo")]
     pub fn set_in_style_for_servo(&self, style: &mut ComputedValues) {
         match self {
             % for prop in data.longhands:
@@ -439,6 +439,11 @@ impl AnimationValue {
             % endfor
         }
     }
+
+    /// As above, but a stub for Gecko.
+    #[cfg(feature = "gecko")]
+    pub fn set_in_style_for_servo(&self, _: &mut ComputedValues) {
+    }
 }
 
 fn animate_discrete<T: Clone>(this: &T, other: &T, procedure: Procedure) -> Result<T, ()> {
diff --git a/components/style/selector_map.rs b/components/style/selector_map.rs
index 3c811e2e458..2088a5baab1 100644
--- a/components/style/selector_map.rs
+++ b/components/style/selector_map.rs
@@ -278,9 +278,12 @@ impl SelectorMap<Rule> {
 }
 
 impl<T: SelectorMapEntry> SelectorMap<T> {
-    /// Inserts into the correct hash, trying id, class, localname and
-    /// namespace.
-    pub fn insert(&mut self, entry: T, quirks_mode: QuirksMode) -> Result<(), FailedAllocationError> {
+    /// Inserts an entry into the correct bucket(s).
+    pub fn insert(
+        &mut self,
+        entry: T,
+        quirks_mode: QuirksMode,
+    ) -> Result<(), FailedAllocationError> {
         self.count += 1;
 
         // NOTE(emilio): It'd be nice for this to be a separate function, but
diff --git a/components/style/servo/selector_parser.rs b/components/style/servo/selector_parser.rs
index d8b84b13280..af4dd92fcf7 100644
--- a/components/style/servo/selector_parser.rs
+++ b/components/style/servo/selector_parser.rs
@@ -615,15 +615,14 @@ impl DerefMut for SnapshotMap {
 }
 
 /// Servo's version of an element snapshot.
-#[derive(Debug)]
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
+#[derive(Debug, Default, MallocSizeOf)]
 pub struct ServoElementSnapshot {
     /// The stored state of the element.
     pub state: Option<ElementState>,
     /// The set of stored attributes and its values.
     pub attrs: Option<Vec<(AttrIdentifier, AttrValue)>>,
-    /// Whether this element is an HTML element in an HTML document.
-    pub is_html_element_in_html_document: bool,
+    /// The set of changed attributes and its values.
+    pub changed_attrs: Vec<LocalName>,
     /// Whether the class attribute changed or not.
     pub class_changed: bool,
     /// Whether the id attribute changed or not.
@@ -634,15 +633,8 @@ pub struct ServoElementSnapshot {
 
 impl ServoElementSnapshot {
     /// Create an empty element snapshot.
-    pub fn new(is_html_element_in_html_document: bool) -> Self {
-        ServoElementSnapshot {
-            state: None,
-            attrs: None,
-            is_html_element_in_html_document: is_html_element_in_html_document,
-            class_changed: false,
-            id_changed: false,
-            other_attributes_changed: false,
-        }
+    pub fn new() -> Self {
+        Self::default()
     }
 
     /// Returns whether the id attribute changed or not.
@@ -669,6 +661,17 @@ impl ServoElementSnapshot {
             .map(|&(_, ref v)| v)
     }
 
+    /// Executes the callback once for each attribute that changed.
+    #[inline]
+    pub fn each_attr_changed<F>(&self, mut callback: F)
+    where
+        F: FnMut(&LocalName),
+    {
+        for name in &self.changed_attrs {
+            callback(name)
+        }
+    }
+
     fn any_attr_ignore_ns<F>(&self, name: &LocalName, mut f: F) -> bool
     where
         F: FnMut(&AttrValue) -> bool,
diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
index 107fd6d7103..d151062199f 100644
--- a/components/style/shared_lock.rs
+++ b/components/style/shared_lock.rs
@@ -15,7 +15,6 @@ use std::cell::UnsafeCell;
 use std::fmt;
 #[cfg(feature = "servo")]
 use std::mem;
-use std::mem::ManuallyDrop;
 #[cfg(feature = "gecko")]
 use std::ptr;
 use to_shmem::{SharedMemoryBuilder, ToShmem};
diff --git a/components/style/values/animated/color.rs b/components/style/values/animated/color.rs
index 14b1d0c539c..9f4fa5c52b5 100644
--- a/components/style/values/animated/color.rs
+++ b/components/style/values/animated/color.rs
@@ -12,8 +12,7 @@ use crate::values::generics::color::{Color as GenericColor, ComplexColorRatios};
 ///
 /// Unlike in computed values, each component value may exceed the
 /// range `[0.0, 1.0]`.
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToAnimatedZero)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedZero)]
 pub struct RGBA {
     /// The red component.
     pub red: f32,
diff --git a/components/style/values/computed/align.rs b/components/style/values/computed/align.rs
index 893f6fcce51..5cfb53f89ee 100644
--- a/components/style/values/computed/align.rs
+++ b/components/style/values/computed/align.rs
@@ -35,7 +35,7 @@ pub use super::specified::{AlignSelf, JustifySelf};
 /// sucks :(.
 ///
 /// See the discussion in https://bugzil.la/1384542.
-#[derive(Clone, Copy, Debug, Eq, PartialEq, ToCss, ToResolvedValue)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss, ToResolvedValue)]
 #[repr(C)]
 pub struct ComputedJustifyItems {
     /// The specified value for the property. Can contain the bare `legacy`
diff --git a/components/style/values/generics/flex.rs b/components/style/values/generics/flex.rs
index adff13b5b42..85b64000f2b 100644
--- a/components/style/values/generics/flex.rs
+++ b/components/style/values/generics/flex.rs
@@ -5,13 +5,13 @@
 //! Generic types for CSS values related to flexbox.
 
 /// A generic value for the `flex-basis` property.
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(
     Animate,
     Clone,
     ComputeSquaredDistance,
     Copy,
     Debug,
+    MallocSizeOf,
     Parse,
     PartialEq,
     SpecifiedValueInfo,
diff --git a/components/style/values/generics/length.rs b/components/style/values/generics/length.rs
index 4183f40a942..bed574861cb 100644
--- a/components/style/values/generics/length.rs
+++ b/components/style/values/generics/length.rs
@@ -174,13 +174,13 @@ impl<LengthPercentage> Size<LengthPercentage> {
 
 /// A generic value for the `max-width` or `max-height` property.
 #[allow(missing_docs)]
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(
     Animate,
     Clone,
     ComputeSquaredDistance,
     Copy,
     Debug,
+    MallocSizeOf,
     PartialEq,
     SpecifiedValueInfo,
     ToAnimatedValue,
diff --git a/components/style_traits/dom.rs b/components/style_traits/dom.rs
index f9844519279..03d5264abf5 100644
--- a/components/style_traits/dom.rs
+++ b/components/style_traits/dom.rs
@@ -13,8 +13,8 @@
 /// Because the script task's GC does not trace layout, node data cannot be safely stored in layout
 /// data structures. Also, layout code tends to be faster when the DOM is not being accessed, for
 /// locality reasons. Using `OpaqueNode` enforces this invariant.
-#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
-#[cfg_attr(feature = "servo", derive(MallocSizeOf, Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub struct OpaqueNode(pub usize);
 
 impl OpaqueNode {
diff --git a/components/url/lib.rs b/components/url/lib.rs
index 8a05837a461..f58bbbad3ff 100644
--- a/components/url/lib.rs
+++ b/components/url/lib.rs
@@ -20,7 +20,6 @@ pub use crate::origin::{ImmutableOrigin, MutableOrigin, OpaqueOrigin};
 use std::collections::hash_map::DefaultHasher;
 use std::fmt;
 use std::hash::Hasher;
-use std::mem::ManuallyDrop;
 use std::net::IpAddr;
 use std::ops::{Index, Range, RangeFrom, RangeFull, RangeTo};
 use std::path::Path;
@@ -34,7 +33,7 @@ pub use url::Host;
 pub struct ServoUrl(#[ignore_malloc_size_of = "Arc"] Arc<Url>);
 
 impl ToShmem for ServoUrl {
-    fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> ManuallyDrop<Self> {
+    fn to_shmem(&self, _builder: &mut SharedMemoryBuilder) -> to_shmem::Result<Self> {
         unimplemented!("If servo wants to share stylesheets across processes, ToShmem for Url must be implemented")
     }
 }