diff --git a/Cargo.lock b/Cargo.lock
index 0947a17da29..3a4572ebab8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3737,12 +3737,11 @@ dependencies = [
 
 [[package]]
 name = "html5ever"
-version = "0.33.0"
+version = "0.35.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d485f1d312f0938f1d8c175a115a1e9f357f8b63262a043b66ce11e1e48128b"
+checksum = "55d958c2f74b664487a2035fe1dadb032c48718a03b63f3ab0b8537db8549ed4"
 dependencies = [
  "log",
- "mac",
  "markup5ever",
  "match_token",
 ]
@@ -5034,9 +5033,9 @@ dependencies = [
 
 [[package]]
 name = "markup5ever"
-version = "0.16.2"
+version = "0.35.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2e4cd8c02f18a011991a039855480c64d74291c5792fcc160d55d77dc4de4a39"
+checksum = "311fe69c934650f8f19652b3946075f0fc41ad8757dbb68f1ca14e7900ecc1c3"
 dependencies = [
  "log",
  "tendril",
@@ -5045,9 +5044,9 @@ dependencies = [
 
 [[package]]
 name = "match_token"
-version = "0.2.0"
+version = "0.35.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "69c8968ae498413293a741c58ef9dc583a4d77a3d7eae7f80eedfe3acf667e7f"
+checksum = "ac84fd3f360fcc43dc5f5d186f02a94192761a080e8bc58621ad4d12296a58cf"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -10329,12 +10328,11 @@ checksum = "a62ce76d9b56901b19a74f19431b0d8b3bc7ca4ad685a746dfd78ca8f4fc6bda"
 
 [[package]]
 name = "xml5ever"
-version = "0.22.1"
+version = "0.35.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0a91563ba5a5ab749488164063f1317e327ca1daa80f00e5bd1e670ad0d78154"
+checksum = "ee3f1e41afb31a75aef076563b0ad3ecc24f5bd9d12a72b132222664eb76b494"
 dependencies = [
  "log",
- "mac",
  "markup5ever",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index 6d863656b7c..1e4b8532354 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -71,7 +71,7 @@ gstreamer-video = "0.23"
 harfbuzz-sys = "0.6.1"
 headers = "0.4"
 hitrace = "0.1.5"
-html5ever = "0.33"
+html5ever = "0.35"
 http = "1.3"
 http-body-util = "0.1"
 hyper = "1.6"
@@ -92,7 +92,7 @@ log = "0.4"
 mach2 = "0.4"
 malloc_size_of = { package = "servo_malloc_size_of", path = "components/malloc_size_of" }
 malloc_size_of_derive = "0.1"
-markup5ever = "0.16.2"
+markup5ever = "0.35"
 memmap2 = "0.9.5"
 mime = "0.3.13"
 mime_guess = "2.0.5"
@@ -177,7 +177,7 @@ windows-sys = "0.59"
 wio = "0.2"
 wr_malloc_size_of = { git = "https://github.com/servo/webrender", branch = "0.67" }
 xi-unicode = "0.3.0"
-xml5ever = "0.22"
+xml5ever = "0.35"
 
 [profile.release]
 opt-level = 3
diff --git a/components/script/dom/servoparser/async_html.rs b/components/script/dom/servoparser/async_html.rs
index 21920041af0..0c40e77361e 100644
--- a/components/script/dom/servoparser/async_html.rs
+++ b/components/script/dom/servoparser/async_html.rs
@@ -579,7 +579,7 @@ impl Tokenizer {
             } => {
                 let location = self.get_node(&location);
                 let template = self.get_node(&template);
-                let attributes = attributes
+                let attributes: Vec<_> = attributes
                     .into_iter()
                     .map(|attribute| HtmlAttribute {
                         name: attribute.name,
@@ -588,7 +588,7 @@ impl Tokenizer {
                     .collect();
 
                 let did_succeed =
-                    attach_declarative_shadow_inner(&location, &template, attributes).is_ok();
+                    attach_declarative_shadow_inner(&location, &template, &attributes);
                 sender.send(did_succeed).unwrap();
             },
         }
@@ -610,7 +610,6 @@ fn run(
     scripting_enabled: bool,
 ) {
     let options = TreeBuilderOpts {
-        ignore_missing_rules: true,
         scripting_enabled,
         ..Default::default()
     };
@@ -962,13 +961,13 @@ impl TreeSink for Sink {
         &self,
         location: &Self::Handle,
         template: &Self::Handle,
-        attributes: Vec<HtmlAttribute>,
-    ) -> Result<(), String> {
+        attributes: &[HtmlAttribute],
+    ) -> bool {
         let attributes = attributes
-            .into_iter()
+            .iter()
             .map(|attribute| Attribute {
-                name: attribute.name,
-                value: String::from(attribute.value),
+                name: attribute.name.clone(),
+                value: String::from(attribute.value.clone()),
             })
             .collect();
 
@@ -983,13 +982,6 @@ impl TreeSink for Sink {
             sender,
         });
 
-        let did_succeed = receiver.recv().unwrap();
-
-        // TODO: This api is silly, we shouldn't have to return a string here
-        if did_succeed {
-            Ok(())
-        } else {
-            Err("Attaching declarative shadow root failed".to_owned())
-        }
+        receiver.recv().unwrap()
     }
 }
diff --git a/components/script/dom/servoparser/html.rs b/components/script/dom/servoparser/html.rs
index dd5be7d2b8f..d431f065e9d 100644
--- a/components/script/dom/servoparser/html.rs
+++ b/components/script/dom/servoparser/html.rs
@@ -67,7 +67,6 @@ impl Tokenizer {
         };
 
         let options = TreeBuilderOpts {
-            ignore_missing_rules: true,
             scripting_enabled: document.scripting_enabled(),
             iframe_srcdoc: document.url().as_str() == "about:srcdoc",
             quirks_mode,
diff --git a/components/script/dom/servoparser/mod.rs b/components/script/dom/servoparser/mod.rs
index f0394a62a04..f2bbcac16c6 100644
--- a/components/script/dom/servoparser/mod.rs
+++ b/components/script/dom/servoparser/mod.rs
@@ -1448,9 +1448,9 @@ impl TreeSink for Sink {
         &self,
         host: &Dom<Node>,
         template: &Dom<Node>,
-        attrs: Vec<Attribute>,
-    ) -> Result<(), String> {
-        attach_declarative_shadow_inner(host, template, attrs)
+        attributes: &[Attribute],
+    ) -> bool {
+        attach_declarative_shadow_inner(host, template, attributes)
     }
 }
 
@@ -1588,15 +1588,11 @@ impl TendrilSink<UTF8> for NetworkSink {
     }
 }
 
-fn attach_declarative_shadow_inner(
-    host: &Node,
-    template: &Node,
-    attrs: Vec<Attribute>,
-) -> Result<(), String> {
+fn attach_declarative_shadow_inner(host: &Node, template: &Node, attributes: &[Attribute]) -> bool {
     let host_element = host.downcast::<Element>().unwrap();
 
     if host_element.shadow_root().is_some() {
-        return Err(String::from("Already in a shadow host"));
+        return false;
     }
 
     let template_element = template.downcast::<HTMLTemplateElement>().unwrap();
@@ -1612,13 +1608,17 @@ fn attach_declarative_shadow_inner(
     let mut delegatesfocus = false;
     let mut serializable = false;
 
-    let attrs: Vec<ElementAttribute> = attrs
-        .clone()
-        .into_iter()
-        .map(|attr| ElementAttribute::new(attr.name, DOMString::from(String::from(attr.value))))
+    let attributes: Vec<ElementAttribute> = attributes
+        .iter()
+        .map(|attr| {
+            ElementAttribute::new(
+                attr.name.clone(),
+                DOMString::from(String::from(attr.value.clone())),
+            )
+        })
         .collect();
 
-    attrs
+    attributes
         .iter()
         .for_each(|attr: &ElementAttribute| match attr.name.local {
             local_name!("shadowrootmode") => {
@@ -1664,8 +1664,8 @@ fn attach_declarative_shadow_inner(
             // Step 8.5. Set shadow’s available to element internals to true.
             shadow_root.set_available_to_element_internals(true);
 
-            Ok(())
+            true
         },
-        Err(_) => Err(String::from("Attaching shadow fails")),
+        Err(_) => false,
     }
 }