diff --git a/components/script/dom/domtokenlist.rs b/components/script/dom/domtokenlist.rs
index 7ee5e632900..0a42db03d5d 100644
--- a/components/script/dom/domtokenlist.rs
+++ b/components/script/dom/domtokenlist.rs
@@ -159,4 +159,9 @@ impl<'a> DOMTokenListMethods for JSRef<'a, DOMTokenList> {
             }
         }
     }
+
+    // https://dom.spec.whatwg.org/#stringification-behavior
+    fn Stringifier(self) -> DOMString {
+        self.element.root().r().get_string_attribute(&self.local_name)
+    }
 }
diff --git a/components/script/dom/urlsearchparams.rs b/components/script/dom/urlsearchparams.rs
index f19e936ce54..91c25794716 100644
--- a/components/script/dom/urlsearchparams.rs
+++ b/components/script/dom/urlsearchparams.rs
@@ -106,6 +106,11 @@ impl<'a> URLSearchParamsMethods for JSRef<'a, URLSearchParams> {
         self.data.borrow_mut().insert(name, vec!(value));
         self.update_steps();
     }
+
+    // https://url.spec.whatwg.org/#stringification-behavior
+    fn Stringifier(self) -> DOMString {
+        DOMString::from_utf8(self.serialize(None)).unwrap()
+    }
 }
 
 pub trait URLSearchParamsHelpers {
diff --git a/components/script/dom/webidls/DOMTokenList.webidl b/components/script/dom/webidls/DOMTokenList.webidl
index 764f18d6dfa..61a3bebff15 100644
--- a/components/script/dom/webidls/DOMTokenList.webidl
+++ b/components/script/dom/webidls/DOMTokenList.webidl
@@ -17,5 +17,5 @@ interface DOMTokenList {
   [Throws]
   boolean toggle(DOMString token, optional boolean force);
 
-  //stringifier;
+  stringifier;
 };
diff --git a/components/script/dom/webidls/URLSearchParams.webidl b/components/script/dom/webidls/URLSearchParams.webidl
index 3d61263cbc9..f0ddafad291 100644
--- a/components/script/dom/webidls/URLSearchParams.webidl
+++ b/components/script/dom/webidls/URLSearchParams.webidl
@@ -15,5 +15,5 @@ interface URLSearchParams {
   // sequence<DOMString> getAll(DOMString name);
   boolean has(DOMString name);
   void set(DOMString name, DOMString value);
-  //stringifier;
+  stringifier;
 };
diff --git a/tests/wpt/metadata/dom/interfaces.html.ini b/tests/wpt/metadata/dom/interfaces.html.ini
index 3abf7a55e5d..14ac6621ede 100644
--- a/tests/wpt/metadata/dom/interfaces.html.ini
+++ b/tests/wpt/metadata/dom/interfaces.html.ini
@@ -825,9 +825,6 @@
   [DOMTokenList interface: operation toggle(DOMString,boolean)]
     expected: FAIL
 
-  [DOMTokenList interface: stringifier]
-    expected: FAIL
-
   [DOMTokenList interface: calling add(DOMString) on document.body.classList with too few arguments must throw TypeError]
     expected: FAIL
 
diff --git a/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini b/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
index 9a6f69132ab..2526f96f80b 100644
--- a/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
+++ b/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
@@ -12,42 +12,12 @@
   [classList.add must not cause the CSS selector to stop matching]
     expected: FAIL
 
-  [classList must stringify correctly when items have been added]
-    expected: FAIL
-
-  [classList.add should not add a token if it already exists]
-    expected: FAIL
-
-  [classList.remove removes arguments passed, if they are present.]
-    expected: FAIL
-
-  [classList.remove must remove existing tokens]
-    expected: FAIL
-
   [classList.remove must not break case-sensitive CSS selector matching]
     expected: FAIL
 
-  [classList.remove must collapse whitespace around removed tokens]
-    expected: FAIL
-
-  [classList.remove must collapse whitespaces around each token]
-    expected: FAIL
-
-  [classList.remove must collapse whitespaces around each token and remove duplicates]
-    expected: FAIL
-
-  [classList.remove must collapse whitespace when removing duplicate tokens]
-    expected: FAIL
-
-  [classList.add must collapse whitespaces and remove duplicates when adding a token that already exists]
-    expected: FAIL
-
   [classList.toggle must not break case-sensitive CSS selector matching]
     expected: FAIL
 
   [CSS class selectors must stop matching when all classes have been removed]
     expected: FAIL
 
-  [classList must stringify to an empty string when all classes have been removed]
-    expected: FAIL
-