diff --git a/parser/html/javasrc/ElementName.java b/parser/html/javasrc/ElementName.java
index 5748c3fbf46b..9ee2ad01520d 100644
--- a/parser/html/javasrc/ElementName.java
+++ b/parser/html/javasrc/ElementName.java
@@ -1166,7 +1166,7 @@ public static final ElementName MN = new ElementName("mn", "mn",
 // CPPONLY: NS_NewSVGUnknownElement, 
 TreeBuilder.MI_MO_MN_MS_MTEXT | SCOPING_AS_MATHML);
 public static final ElementName KEYGEN = new ElementName("keygen", "keygen", 
-// CPPONLY: NS_NewHTMLElement,
+// CPPONLY: NS_NewHTMLUnknownElement,
 // CPPONLY: NS_NewSVGUnknownElement, 
 TreeBuilder.KEYGEN | SPECIAL);
 public static final ElementName MAIN = new ElementName("main", "main", 
diff --git a/parser/html/nsHtml5ElementName.cpp b/parser/html/nsHtml5ElementName.cpp
index 3e90b4e7ceab..93a6407d387c 100644
--- a/parser/html/nsHtml5ElementName.cpp
+++ b/parser/html/nsHtml5ElementName.cpp
@@ -787,7 +787,7 @@ void nsHtml5ElementName::initializeStatics() {
       NS_NewSVGUnknownElement,
       nsHtml5TreeBuilder::MI_MO_MN_MS_MTEXT | SCOPING_AS_MATHML);
   ELT_KEYGEN = new nsHtml5ElementName(
-      nsGkAtoms::keygen, nsGkAtoms::keygen, NS_NewHTMLElement,
+      nsGkAtoms::keygen, nsGkAtoms::keygen, NS_NewHTMLUnknownElement,
       NS_NewSVGUnknownElement, nsHtml5TreeBuilder::KEYGEN | SPECIAL);
   ELT_MAIN = new nsHtml5ElementName(
       nsGkAtoms::main, nsGkAtoms::main, NS_NewHTMLElement,
diff --git a/testing/web-platform/meta/html/semantics/interfaces.html.ini b/testing/web-platform/meta/html/semantics/interfaces.html.ini
index 17f5b85ad571..faf9fd40e4d0 100644
--- a/testing/web-platform/meta/html/semantics/interfaces.html.ini
+++ b/testing/web-platform/meta/html/semantics/interfaces.html.ini
@@ -1,8 +1,10 @@
 [interfaces.html]
   prefs: [dom.dialog_element.enabled:true]
-  [Interfaces for image]
+  [Interfaces for image: useNS]
     expected: FAIL
+    bug: 1776081
 
-  [Interfaces for IMAGE]
+  [Interfaces for IMAGE: createElement]
     expected: FAIL
+    bug: 1776081
 
diff --git a/testing/web-platform/tests/html/semantics/interfaces.html b/testing/web-platform/tests/html/semantics/interfaces.html
index 9cb7f5eaef1c..dc7b600e0a0e 100644
--- a/testing/web-platform/tests/html/semantics/interfaces.html
+++ b/testing/web-platform/tests/html/semantics/interfaces.html
@@ -17,6 +17,8 @@ function do_test(local_name, iface, variant) {
     if (variant === "useNS") {
       // Use createElementNS here to preserve the case of local_name.
       e = document.createElementNS("http://www.w3.org/1999/xhtml", local_name);
+    } else if (variant === "useParser") {
+      e = new DOMParser().parseFromString("<" + local_name + ">", "text/html").querySelector(local_name);
     } else {
       e = document.createElement(local_name);
     }
@@ -31,17 +33,42 @@ function do_test(local_name, iface, variant) {
                 "Element " + local_name + " should implement Element.");
     assert_true(e instanceof Node,
                 "Element " + local_name + " should implement Node.");
-  }, "Interfaces for " + local_name);
+  }, "Interfaces for " + local_name + ": " + variant);
+}
+
+// Some elements have weird parser behavior / insertion modes and would be
+// skipped by the parser, so skip those.
+function should_do_parser_test(local_name) {
+  return ![
+    "foo-BAR",
+    "tbody",
+    "td",
+    "tfoot",
+    "th",
+    "thead",
+    "tr",
+    "å-bar",
+    "caption",
+    "col",
+    "colgroup",
+    "frame",
+    "image",
+    "frameset",
+  ].includes(local_name)
 }
 
 elements.forEach(function(a) {
   do_test(a[0], a[1], "useNS");
 
+  if (should_do_parser_test(a[0])) {
+    do_test(a[0], a[1], "useParser");
+  }
+
   // Only run the createElement variant if the input is all-lowercase, because createElement
   // case-folds to lowercase. Custom elements are required to use all-lowercase to implement
   // HTMLElement, otherwise they use HTMLUnknownElement per spec. Example: "foo-BAR".
   if (a[0] === a[0].toLowerCase()) {
-    do_test(a[0].toUpperCase(), a[1]);
+    do_test(a[0].toUpperCase(), a[1], "createElement");
   }
 })
 </script>