diff --git a/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.cpp b/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.cpp
index aedb266894..f180736878 100644
--- a/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.cpp
+++ b/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.cpp
@@ -16,16 +16,16 @@ namespace Web::CSS {
 
 JS_DEFINE_ALLOCATOR(CSSNamespaceRule);
 
-CSSNamespaceRule::CSSNamespaceRule(JS::Realm& realm, Optional<DeprecatedString> prefix, StringView namespace_uri)
+CSSNamespaceRule::CSSNamespaceRule(JS::Realm& realm, Optional<FlyString> prefix, FlyString namespace_uri)
     : CSSRule(realm)
-    , m_namespace_uri(namespace_uri)
-    , m_prefix(prefix.value_or(""sv))
+    , m_namespace_uri(move(namespace_uri))
+    , m_prefix(prefix.value_or(""_fly_string))
 {
 }
 
-JS::NonnullGCPtr<CSSNamespaceRule> CSSNamespaceRule::create(JS::Realm& realm, Optional<DeprecatedString> prefix, AK::StringView namespace_uri)
+JS::NonnullGCPtr<CSSNamespaceRule> CSSNamespaceRule::create(JS::Realm& realm, Optional<FlyString> prefix, FlyString namespace_uri)
 {
-    return realm.heap().allocate<CSSNamespaceRule>(realm, realm, prefix, namespace_uri);
+    return realm.heap().allocate<CSSNamespaceRule>(realm, realm, move(prefix), move(namespace_uri));
 }
 
 void CSSNamespaceRule::initialize(JS::Realm& realm)
diff --git a/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.h b/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.h
index 273f8a742a..cf41bef7b3 100644
--- a/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.h
+++ b/Userland/Libraries/LibWeb/CSS/CSSNamespaceRule.h
@@ -15,24 +15,24 @@ class CSSNamespaceRule final : public CSSRule {
     JS_DECLARE_ALLOCATOR(CSSNamespaceRule);
 
 public:
-    [[nodiscard]] static JS::NonnullGCPtr<CSSNamespaceRule> create(JS::Realm&, Optional<DeprecatedString> prefix, StringView namespace_uri);
+    [[nodiscard]] static JS::NonnullGCPtr<CSSNamespaceRule> create(JS::Realm&, Optional<FlyString> prefix, FlyString namespace_uri);
 
     virtual ~CSSNamespaceRule() = default;
 
-    void set_namespace_uri(DeprecatedString value) { m_namespace_uri = move(value); }
-    DeprecatedString namespace_uri() const { return m_namespace_uri; }
-    void set_prefix(DeprecatedString value) { m_prefix = move(value); }
-    DeprecatedString prefix() const { return m_prefix; }
+    void set_namespace_uri(FlyString value) { m_namespace_uri = move(value); }
+    FlyString const& namespace_uri() const { return m_namespace_uri; }
+    void set_prefix(FlyString value) { m_prefix = move(value); }
+    FlyString const& prefix() const { return m_prefix; }
     virtual Type type() const override { return Type::Namespace; }
 
 private:
-    CSSNamespaceRule(JS::Realm&, Optional<DeprecatedString> prefix, StringView namespace_uri);
+    CSSNamespaceRule(JS::Realm&, Optional<FlyString> prefix, FlyString namespace_uri);
 
     virtual void initialize(JS::Realm&) override;
 
     virtual String serialized() const override;
-    DeprecatedString m_namespace_uri;
-    DeprecatedString m_prefix;
+    FlyString m_namespace_uri;
+    FlyString m_prefix;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/CSS/CSSStyleSheet.cpp b/Userland/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
index 0af9dc79e2..2735778f1d 100644
--- a/Userland/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
+++ b/Userland/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
@@ -149,7 +149,7 @@ void CSSStyleSheet::set_style_sheet_list(Badge<StyleSheetList>, StyleSheetList*
 Optional<FlyString> CSSStyleSheet::default_namespace() const
 {
     if (m_default_namespace_rule)
-        return MUST(FlyString::from_deprecated_fly_string(m_default_namespace_rule->namespace_uri()));
+        return m_default_namespace_rule->namespace_uri();
 
     return {};
 }
@@ -158,7 +158,7 @@ Optional<FlyString> CSSStyleSheet::namespace_uri(StringView namespace_prefix) co
 {
     return m_namespace_rules.get(namespace_prefix)
         .map([](JS::GCPtr<CSSNamespaceRule> namespace_) {
-            return MUST(FlyString::from_deprecated_fly_string(namespace_->namespace_uri()));
+            return namespace_->namespace_uri();
         });
 }
 
@@ -189,7 +189,7 @@ void CSSStyleSheet::recalculate_namespaces()
         if (!namespace_rule.namespace_uri().is_empty() && namespace_rule.prefix().is_empty())
             m_default_namespace_rule = namespace_rule;
 
-        m_namespace_rules.set(FlyString::from_deprecated_fly_string(namespace_rule.prefix()).release_value_but_fixme_should_propagate_errors(), namespace_rule);
+        m_namespace_rules.set(namespace_rule.prefix(), namespace_rule);
     }
 }
 
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index 80715887d4..c5305d6f53 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1358,18 +1358,18 @@ CSSRule* Parser::convert_to_rule(NonnullRefPtr<Rule> rule)
             token_stream.skip_whitespace();
 
             auto token = token_stream.next_token();
-            Optional<DeprecatedString> prefix = {};
+            Optional<FlyString> prefix = {};
             if (token.is(Token::Type::Ident)) {
-                prefix = token.token().ident().bytes_as_string_view();
+                prefix = token.token().ident();
                 token_stream.skip_whitespace();
                 token = token_stream.next_token();
             }
 
-            DeprecatedString namespace_uri;
+            FlyString namespace_uri;
             if (token.is(Token::Type::String)) {
-                namespace_uri = token.token().string();
+                namespace_uri = MUST(FlyString::from_utf8(token.token().string()));
             } else if (auto url = parse_url_function(token); url.has_value()) {
-                namespace_uri = url.value().to_deprecated_string();
+                namespace_uri = MUST(FlyString::from_deprecated_fly_string(url.value().to_deprecated_string()));
             } else {
                 dbgln_if(CSS_PARSER_DEBUG, "CSSParser: @namespace rule invalid; discarding.");
                 return {};