diff --git a/crates/web-sys/Cargo.toml b/crates/web-sys/Cargo.toml
index 5ad947b0..51165e0b 100644
--- a/crates/web-sys/Cargo.toml
+++ b/crates/web-sys/Cargo.toml
@@ -38,7 +38,10 @@ wasm-bindgen-futures = { path = '../futures', version = '0.2.21' }
 AbortController = []
 AbortSignal = []
 AddEventListenerOptions = []
+AesCbcParams = []
+AesCtrParams = []
 AesDerivedKeyParams = []
+AesGcmParams = []
 AesKeyAlgorithm = []
 AesKeyGenParams = []
 Algorithm = []
@@ -289,10 +292,12 @@ Element = []
 ElementCreationOptions = []
 ElementDefinitionOptions = []
 EndingTypes = []
+ErrorCallback = []
 ErrorEvent = []
 ErrorEventInit = []
 Event = []
 EventInit = []
+EventListener = []
 EventListenerOptions = []
 EventModifierInit = []
 EventSource = []
@@ -310,6 +315,7 @@ FetchReadableStreamReadDataArray = []
 FetchReadableStreamReadDataDone = []
 FetchState = []
 File = []
+FileCallback = []
 FileList = []
 FilePropertyBag = []
 FileReader = []
@@ -317,7 +323,9 @@ FileReaderSync = []
 FileSystem = []
 FileSystemDirectoryEntry = []
 FileSystemDirectoryReader = []
+FileSystemEntriesCallback = []
 FileSystemEntry = []
+FileSystemEntryCallback = []
 FileSystemFileEntry = []
 FileSystemFlags = []
 FillMode = []
@@ -602,6 +610,7 @@ NetworkCommandOptions = []
 NetworkInformation = []
 NetworkResultOptions = []
 Node = []
+NodeFilter = []
 NodeIterator = []
 NodeList = []
 Notification = []
@@ -611,6 +620,7 @@ NotificationEvent = []
 NotificationEventInit = []
 NotificationOptions = []
 NotificationPermission = []
+ObserverCallback = []
 OfflineAudioCompletionEvent = []
 OfflineAudioCompletionEventInit = []
 OfflineAudioContext = []
@@ -702,10 +712,13 @@ ProgressEventInit = []
 PromiseRejectionEvent = []
 PromiseRejectionEventInit = []
 PublicKeyCredential = []
+PublicKeyCredentialDescriptor = []
 PublicKeyCredentialEntity = []
 PublicKeyCredentialParameters = []
+PublicKeyCredentialRequestOptions = []
 PublicKeyCredentialRpEntity = []
 PublicKeyCredentialType = []
+PublicKeyCredentialUserEntity = []
 PushEncryptionKeyName = []
 PushEvent = []
 PushEventInit = []
@@ -768,6 +781,7 @@ RtcIceServer = []
 RtcIceTransportPolicy = []
 RtcIdentityAssertion = []
 RtcIdentityAssertionResult = []
+RtcIdentityProvider = []
 RtcIdentityProviderDetails = []
 RtcIdentityProviderOptions = []
 RtcIdentityValidationResult = []
@@ -1038,6 +1052,7 @@ VideoPlaybackQuality = []
 VideoStreamTrack = []
 VideoTrack = []
 VideoTrackList = []
+VoidCallback = []
 VrDisplay = []
 VrDisplayCapabilities = []
 VrEye = []
@@ -1170,6 +1185,7 @@ WorkerOptions = []
 Worklet = []
 WorkletGlobalScope = []
 XPathExpression = []
+XPathNsResolver = []
 XPathResult = []
 XmlDocument = []
 XmlHttpRequest = []
diff --git a/crates/web-sys/webidls/enabled/EventTarget.webidl b/crates/web-sys/webidls/enabled/EventTarget.webidl
index c5fb9587..000f44bc 100644
--- a/crates/web-sys/webidls/enabled/EventTarget.webidl
+++ b/crates/web-sys/webidls/enabled/EventTarget.webidl
@@ -29,12 +29,12 @@ interface EventTarget {
      false. */
   [Throws]
   void addEventListener(DOMString type,
-                        EventListener? listener,
+                        EventListener listener,
                         optional (AddEventListenerOptions or boolean) options,
                         optional boolean? wantsUntrusted = null);
   [Throws]
   void removeEventListener(DOMString type,
-                           EventListener? listener,
+                           EventListener listener,
                            optional (EventListenerOptions or boolean) options);
   [Throws, NeedsCallerType]
   boolean dispatchEvent(Event event);
diff --git a/crates/webidl-tests/callbacks.js b/crates/webidl-tests/callbacks.js
new file mode 100644
index 00000000..b976bfd3
--- /dev/null
+++ b/crates/webidl-tests/callbacks.js
@@ -0,0 +1,4 @@
+global.TakeCallbackInterface = class {
+  a() {}
+  b() {}
+};
diff --git a/crates/webidl-tests/callbacks.rs b/crates/webidl-tests/callbacks.rs
new file mode 100644
index 00000000..baa36af9
--- /dev/null
+++ b/crates/webidl-tests/callbacks.rs
@@ -0,0 +1,38 @@
+use wasm_bindgen_test::*;
+use js_sys::Function;
+
+include!(concat!(env!("OUT_DIR"), "/callbacks.rs"));
+
+#[wasm_bindgen_test]
+fn multi_op_same_name() {
+    let a = CallbackInterface2::new();
+    let b = TakeCallbackInterface::new().unwrap();
+    b.b(&a);
+}
+
+#[wasm_bindgen_test]
+fn single_op_function() {
+    let a = Function::new_no_args("");
+    let b = TakeCallbackInterface::new().unwrap();
+    b.a_with_callback(&a);
+}
+
+#[wasm_bindgen_test]
+fn single_op_dict() {
+    let a = CallbackInterface1::new();
+    let b = TakeCallbackInterface::new().unwrap();
+    b.a_with_callback_interface1(&a);
+}
+
+#[wasm_bindgen_test]
+fn dict_methods() {
+    let mut a = CallbackInterface1::new();
+    a.foo(&Function::new_no_args(""));
+}
+
+#[wasm_bindgen_test]
+fn dict_methods1() {
+    let mut a = CallbackInterface2::new();
+    a.foo(&Function::new_no_args(""));
+    a.bar(&Function::new_no_args(""));
+}
diff --git a/crates/webidl-tests/callbacks.webidl b/crates/webidl-tests/callbacks.webidl
new file mode 100644
index 00000000..26227afb
--- /dev/null
+++ b/crates/webidl-tests/callbacks.webidl
@@ -0,0 +1,14 @@
+callback interface CallbackInterface1 {
+  void foo();
+};
+
+callback interface CallbackInterface2 {
+  void foo();
+  void bar();
+};
+
+[Constructor()]
+interface TakeCallbackInterface {
+  void a(CallbackInterface1 arg);
+  void b(CallbackInterface2 arg);
+};
diff --git a/crates/webidl-tests/main.rs b/crates/webidl-tests/main.rs
index 66266567..2e20392a 100644
--- a/crates/webidl-tests/main.rs
+++ b/crates/webidl-tests/main.rs
@@ -11,3 +11,4 @@ pub mod simple;
 pub mod throws;
 pub mod dictionary;
 pub mod global;
+pub mod callbacks;
diff --git a/crates/webidl/src/first_pass.rs b/crates/webidl/src/first_pass.rs
index 1b19d8a1..75a4ca11 100644
--- a/crates/webidl/src/first_pass.rs
+++ b/crates/webidl/src/first_pass.rs
@@ -12,6 +12,7 @@ use std::collections::{BTreeMap, BTreeSet};
 
 use proc_macro2::Ident;
 use weedle::{DictionaryDefinition, PartialDictionaryDefinition};
+use weedle::CallbackInterfaceDefinition;
 use weedle::argument::Argument;
 use weedle::attribute::*;
 use weedle::interface::*;
@@ -35,6 +36,7 @@ pub(crate) struct FirstPassRecord<'src> {
     pub(crate) includes: BTreeMap<&'src str, BTreeSet<&'src str>>,
     pub(crate) dictionaries: BTreeMap<&'src str, DictionaryData<'src>>,
     pub(crate) callbacks: BTreeSet<&'src str>,
+    pub(crate) callback_interfaces: BTreeMap<&'src str, CallbackInterfaceData<'src>>,
 }
 
 /// We need to collect interface data during the first pass, to be used later.
@@ -64,17 +66,20 @@ pub(crate) struct MixinData<'src> {
 /// We need to collect namespace data during the first pass, to be used later.
 #[derive(Default)]
 pub(crate) struct NamespaceData<'src> {
-    /// Whether only partial namespaces were encountered
     pub(crate) operations: BTreeMap<OperationId<'src>, OperationData<'src>>,
 }
 
 #[derive(Default)]
 pub(crate) struct DictionaryData<'src> {
-    /// Whether only partial namespaces were encountered
     pub(crate) partials: Vec<&'src PartialDictionaryDefinition<'src>>,
     pub(crate) definition: Option<&'src DictionaryDefinition<'src>>,
 }
 
+pub(crate) struct CallbackInterfaceData<'src> {
+    pub(crate) definition: &'src CallbackInterfaceDefinition<'src>,
+    pub(crate) single_function: bool,
+}
+
 #[derive(PartialEq, Eq, PartialOrd, Ord, Debug, Clone, Copy)]
 pub(crate) enum OperationId<'src> {
     Constructor(IgnoreTraits<&'src str>),
@@ -137,12 +142,8 @@ impl<'src> FirstPass<'src, ()> for weedle::Definition<'src> {
             PartialNamespace(namespace) => namespace.first_pass(record, ()),
             Typedef(typedef) => typedef.first_pass(record, ()),
             Callback(callback) => callback.first_pass(record, ()),
-
+            CallbackInterface(iface) => iface.first_pass(record, ()),
             Implements(_) => Ok(()),
-            CallbackInterface(..) => {
-                warn!("Unsupported WebIDL CallbackInterface definition: {:?}", self);
-                Ok(())
-            }
         }
     }
 }
@@ -690,6 +691,25 @@ impl<'src> FirstPass<'src, ()> for weedle::CallbackDefinition<'src> {
     }
 }
 
+impl<'src> FirstPass<'src, ()> for weedle::CallbackInterfaceDefinition<'src> {
+    fn first_pass(&'src self, record: &mut FirstPassRecord<'src>, _: ()) -> Result<()> {
+        if util::is_chrome_only(&self.attributes) {
+            return Ok(())
+        }
+        if self.inheritance.is_some() {
+            warn!("skipping callback interface with inheritance: {}",
+                  self.identifier.0);
+            return Ok(())
+        }
+        let data = CallbackInterfaceData {
+            definition: self,
+            single_function: self.members.body.len() == 1,
+        };
+        record.callback_interfaces.insert(self.identifier.0, data);
+        Ok(())
+    }
+}
+
 impl<'a> FirstPassRecord<'a> {
     pub fn all_superclasses<'me>(&'me self, interface: &str)
         -> impl Iterator<Item = String> + 'me
diff --git a/crates/webidl/src/idl_type.rs b/crates/webidl/src/idl_type.rs
index ec525e91..5e03e96d 100644
--- a/crates/webidl/src/idl_type.rs
+++ b/crates/webidl/src/idl_type.rs
@@ -48,6 +48,7 @@ pub(crate) enum IdlType<'a> {
     Interface(&'a str),
     Dictionary(&'a str),
     Enum(&'a str),
+    CallbackInterface { name: &'a str, single_function: bool },
 
     Nullable(Box<IdlType<'a>>),
     FrozenArray(Box<IdlType<'a>>),
@@ -296,6 +297,11 @@ impl<'a> ToIdlType<'a> for Identifier<'a> {
             Some(IdlType::Enum(self.0))
         } else if record.callbacks.contains(self.0) {
             Some(IdlType::Callback)
+        } else if let Some(data) = record.callback_interfaces.get(self.0) {
+            Some(IdlType::CallbackInterface {
+                name: self.0,
+                single_function: data.single_function,
+            })
         } else {
             warn!("Unrecognized type: {}", self.0);
             None
@@ -387,6 +393,9 @@ impl<'a> IdlType<'a> {
             IdlType::Interface(name) => dst.push_str(&snake_case_ident(name)),
             IdlType::Dictionary(name) => dst.push_str(&snake_case_ident(name)),
             IdlType::Enum(name) => dst.push_str(&snake_case_ident(name)),
+            IdlType::CallbackInterface { name, .. } => {
+                dst.push_str(&snake_case_ident(name))
+            }
 
             IdlType::Nullable(idl_type) => {
                 dst.push_str("opt_");
@@ -480,7 +489,8 @@ impl<'a> IdlType<'a> {
 
             IdlType::ArrayBufferView | IdlType::BufferSource => js_sys("Object"),
             IdlType::Interface(name)
-            | IdlType::Dictionary(name) => {
+            | IdlType::Dictionary(name)
+            | IdlType::CallbackInterface { name, .. } => {
                 let ty = ident_ty(rust_ident(camel_case_ident(name).as_str()));
                 if pos == TypePosition::Argument {
                     Some(shared_ref(ty, false))
@@ -588,6 +598,17 @@ impl<'a> IdlType<'a> {
             IdlType::UnsignedLongLong => {
                 vec![IdlType::UnsignedLong, IdlType::Double]
             }
+            IdlType::CallbackInterface { name, single_function: true } => {
+                // According to the webidl spec [1] single-function callback
+                // interfaces can also be replaced in arguments with simply a
+                // single callable function, which we map to a `Callback`.
+                //
+                // [1]: https://heycam.github.io/webidl/#es-user-objects
+                vec![
+                    IdlType::Callback,
+                    IdlType::CallbackInterface { name, single_function: false },
+                ]
+            }
             idl_type @ _ => vec![idl_type.clone()],
         }
     }
diff --git a/crates/webidl/src/lib.rs b/crates/webidl/src/lib.rs
index 51a3c9c2..092ef92b 100644
--- a/crates/webidl/src/lib.rs
+++ b/crates/webidl/src/lib.rs
@@ -42,9 +42,10 @@ use backend::util::{ident_ty, rust_ident, raw_ident, wrap_import_function};
 use proc_macro2::{Ident, Span};
 use weedle::attribute::{ExtendedAttributeList};
 use weedle::dictionary::DictionaryMember;
+use weedle::interface::InterfaceMember;
 
 use first_pass::{FirstPass, FirstPassRecord, OperationId, InterfaceData};
-use first_pass::OperationData;
+use first_pass::{OperationData, CallbackInterfaceData};
 use util::{public, webidl_const_v_to_backend_const_v, TypePosition, camel_case_ident, shouty_snake_case_ident, snake_case_ident, mdn_doc};
 use idl_type::ToIdlType;
 
@@ -108,6 +109,11 @@ fn parse(webidl_source: &str, allowed_types: Option<&[&str]>)
             first_pass_record.append_interface(&mut program, name, d);
         }
     }
+    for (name, d) in first_pass_record.callback_interfaces.iter() {
+        if filter(name) {
+            first_pass_record.append_callback_interface(&mut program, d);
+        }
+    }
 
     // Prune out `extends` annotations that aren't defined as these shouldn't
     // prevent the type from being usable entirely. They're just there for
@@ -644,4 +650,38 @@ impl<'src> FirstPassRecord<'src> {
             list,
         ));
     }
+
+    fn append_callback_interface(
+        &self,
+        program: &mut backend::ast::Program,
+        item: &CallbackInterfaceData<'src>,
+    ) {
+        let mut fields = Vec::new();
+        for member in item.definition.members.body.iter() {
+            match member {
+                InterfaceMember::Operation(op) => {
+                    let identifier = match op.identifier {
+                        Some(i) => i.0,
+                        None => continue,
+                    };
+                    let pos = TypePosition::Argument;
+                    fields.push(ast::DictionaryField {
+                        required: false,
+                        name: rust_ident(&snake_case_ident(identifier)),
+                        ty: idl_type::IdlType::Callback.to_syn_type(pos)
+                            .unwrap(),
+                    });
+                }
+                _ => {
+                    warn!("skipping callback interface member on {}",
+                          item.definition.identifier.0);
+                }
+            }
+        }
+
+        program.dictionaries.push(ast::Dictionary {
+            name: rust_ident(&camel_case_ident(item.definition.identifier.0)),
+            fields,
+        });
+    }
 }