--- a/dom/base/Location.cpp
+++ b/dom/base/Location.cpp
@@ -709,16 +709,33 @@ Location::SetProtocol(const nsAString& a
     return rv;
   }
   // We may want a new URI class for the new URI, so recreate it:
   rv = NS_NewURI(getter_AddRefs(uri), newSpec);
   if (NS_FAILED(rv)) {
     return rv;
   }
 
+  bool isHttp;
+  rv = uri->SchemeIs("http", &isHttp);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  bool isHttps;
+  rv = uri->SchemeIs("https", &isHttps);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (!isHttp && !isHttps) {
+    // No-op, per spec.
+    return NS_OK;
+  }
+
   return SetURI(uri);
 }
 
 NS_IMETHODIMP
 Location::GetSearch(nsAString& aSearch)
 {
   aSearch.SetLength(0);
 

--- a/testing/web-platform/meta/html/browsers/history/the-location-interface/location-protocol-setter-non-broken-weird.html.ini
+++ b/testing/web-platform/meta/html/browsers/history/the-location-interface/location-protocol-setter-non-broken-weird.html.ini
@@ -1,5 +1,5 @@
 [location-protocol-setter-non-broken-weird.html]
   type: testharness
-  [Set location.protocol to x]
+  [Set location.protocol to data]
     expected: FAIL
 

--- a/testing/web-platform/meta/html/browsers/history/the-location-interface/location-protocol-setter-non-broken.html.ini
+++ b/testing/web-platform/meta/html/browsers/history/the-location-interface/location-protocol-setter-non-broken.html.ini
@@ -1,37 +1,5 @@
 [location-protocol-setter-non-broken.html]
   type: testharness
-  disabled: https://github.com/w3c/web-platform-tests/issues/4720
-  expected: OK
-  [Set HTTP URL frame location.protocol to x]
-    expected: FAIL
-
-  [Set data URL frame location.protocol to x]
-    expected: FAIL
-
   [Set HTTP URL frame location.protocol to data]
     expected: FAIL
 
-  [Set data URL frame location.protocol to data]
-    expected: PASS
-
-  [Set HTTP URL frame location.protocol to file]
-    expected: FAIL
-
-  [Set data URL frame location.protocol to file]
-    expected: FAIL
-
-  [Set data URL frame location.protocol to ftp]
-    expected: PASS
-
-  [Set HTTP URL frame location.protocol to gopher]
-    expected: FAIL
-
-  [Set data URL frame location.protocol to gopher]
-    expected: FAIL
-
-  [Set HTTP URL frame location.protocol to http+x]
-    expected: FAIL
-
-  [Set data URL frame location.protocol to http+x]
-    expected: FAIL
-