diff --git a/lighthouse-cli/test/fixtures/static-server.js b/lighthouse-cli/test/fixtures/static-server.js
index 69e1c3c9148f..86f4e35d58e2 100644
--- a/lighthouse-cli/test/fixtures/static-server.js
+++ b/lighthouse-cli/test/fixtures/static-server.js
@@ -12,6 +12,7 @@ const path = require('path');
 const fs = require('fs');
 const parseQueryString = require('querystring').parse;
 const parseURL = require('url').parse;
+const URLSearchParams = require('../../../lighthouse-core/lib/url-shim').URLSearchParams;
 const HEADER_SAFELIST = new Set(['x-robots-tag', 'link']);
 
 const lhRootDirPath = path.join(__dirname, '../../../');
@@ -64,32 +65,29 @@ function requestHandler(request, response) {
 
     let delay = 0;
     if (queryString) {
+      const params = new URLSearchParams(queryString);
       // set document status-code
-      if (typeof queryString.status_code !== 'undefined') {
-        statusCode = parseInt(queryString.status_code, 10);
+      if (params.has('status_code')) {
+        statusCode = parseInt(params.get('status_code'), 10);
       }
 
       // set delay of request when present
-      if (typeof queryString.delay !== 'undefined') {
-        delay = parseInt(queryString.delay, 10) || 2000;
+      if (params.has('delay')) {
+        delay = parseInt(params.get('delay'), 10) || 2000;
       }
 
-      if (typeof queryString.extra_header !== 'undefined') {
-        let extraHeaders = queryString.extra_header;
-        extraHeaders = Array.isArray(extraHeaders) ? extraHeaders : [extraHeaders];
-
-        extraHeaders.forEach(header => {
-          const [headerName, ...headerValue] = header.split(':');
-
+      if (params.has('extra_header')) {
+        const extraHeaders = new URLSearchParams(params.get('extra_header'));
+        for (const [headerName, headerValue] of extraHeaders) {
           if (HEADER_SAFELIST.has(headerName.toLowerCase())) {
-            headers[headerName] = headerValue.join(':');
+            headers[headerName] = headerValue;
           }
-        });
+        }
       }
 
       // redirect url to new url if present
-      if (typeof queryString.redirect !== 'undefined') {
-        return setTimeout(sendRedirect, delay, queryString.redirect);
+      if (params.has('redirect')) {
+        return setTimeout(sendRedirect, delay, params.get('redirect'));
       }
     }
 
diff --git a/lighthouse-cli/test/smokehouse/seo/expectations.js b/lighthouse-cli/test/smokehouse/seo/expectations.js
index ae55871da27f..b63dcd02b879 100644
--- a/lighthouse-cli/test/smokehouse/seo/expectations.js
+++ b/lighthouse-cli/test/smokehouse/seo/expectations.js
@@ -5,20 +5,20 @@
  */
 'use strict';
 const BASE_URL = 'http://localhost:10200/seo/';
+const URLSearchParams = require('../../../../lighthouse-core/lib/url-shim').URLSearchParams;
 
 function headersParam(headers) {
-  return headers
-    .map(({name, value}) => `extra_header=${name}:${encodeURI(value)}`)
-    .join('&');
+  const headerString = new URLSearchParams(headers).toString();
+  return new URLSearchParams([['extra_header', headerString]]).toString();
 }
 
-const failureHeaders = headersParam([{
-  name: 'x-robots-tag',
-  value: 'none',
-}, {
-  name: 'link',
-  value: '<http://example.com>;rel="alternate";hreflang="xx"',
-}]);
+const failureHeaders = headersParam([[
+  'x-robots-tag',
+  'none',
+], [
+  'link',
+  '<http://example.com>;rel="alternate";hreflang="xx"',
+]]);
 
 /**
  * Expected Lighthouse audit values for seo tests
diff --git a/lighthouse-core/lib/url-shim.js b/lighthouse-core/lib/url-shim.js
index 82ec37e621cb..b6d2fa2d3c4c 100644
--- a/lighthouse-core/lib/url-shim.js
+++ b/lighthouse-core/lib/url-shim.js
@@ -18,6 +18,9 @@ const Util = require('../report/v2/renderer/util.js');
 // https://github.com/GoogleChrome/lighthouse/issues/1186
 const URL = (typeof self !== 'undefined' && self.URL) || require('whatwg-url').URL;
 
+URL.URLSearchParams = (typeof self !== 'undefined' && self.URLSearchParams) ||
+    require('whatwg-url').URLSearchParams;
+
 URL.INVALID_URL_DEBUG_STRING =
     'Lighthouse was unable to determine the URL of some script executions. ' +
     'It\'s possible a Chrome extension or other eval\'d code is the source.';
@@ -104,6 +107,9 @@ URL.elideDataURI = function elideDataURI(url) {
 // As a result, the network URL (chrome://chrome/settings/) doesn't match the final document URL (chrome://settings/).
 function rewriteChromeInternalUrl(url) {
   if (!url || !url.startsWith('chrome://')) return url;
+  // Chrome adds a trailing slash to `chrome://` URLs, but the spec does not.
+  //   https://github.com/GoogleChrome/lighthouse/pull/3941#discussion_r154026009
+  if (url.endsWith('/')) url = url.replace(/\/$/, '');
   return url.replace(/^chrome:\/\/chrome\//, 'chrome://');
 }
 
diff --git a/lighthouse-core/test/lib/url-shim-test.js b/lighthouse-core/test/lib/url-shim-test.js
index e14bb1c29429..b07942bd85c6 100644
--- a/lighthouse-core/test/lib/url-shim-test.js
+++ b/lighthouse-core/test/lib/url-shim-test.js
@@ -218,6 +218,15 @@ describe('URL Shim', () => {
       assert.ok(URL.equalWithExcludedFragments(...pair));
     });
 
+    // https://github.com/GoogleChrome/lighthouse/pull/3941#discussion_r154026009
+    it('canonicalizes chrome:// urls without a trailing slash', () => {
+      const pair = [
+        'chrome://version/',
+        'chrome://version',
+      ];
+      assert.ok(URL.equalWithExcludedFragments(...pair));
+    });
+
     it('returns false for invalid URLs', () => {
       assert.ok(!URL.equalWithExcludedFragments('utter nonsense', 'http://example.com'));
     });
diff --git a/package.json b/package.json
index 960a20459641..4c4199b54ca5 100644
--- a/package.json
+++ b/package.json
@@ -96,7 +96,7 @@
     "semver": "^5.3.0",
     "speedline": "1.3.0",
     "update-notifier": "^2.1.0",
-    "whatwg-url": "4.0.0",
+    "whatwg-url": "^6.3.0",
     "ws": "3.3.2",
     "yargs": "3.32.0",
     "yargs-parser": "7.0.0"
diff --git a/yarn.lock b/yarn.lock
index a6ac6b86c6a1..acd7b7047b38 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2691,6 +2691,10 @@ lodash.restparam@^3.0.0:
   version "3.6.1"
   resolved "https://registry.yarnpkg.com/lodash.restparam/-/lodash.restparam-3.6.1.tgz#936a4e309ef330a7645ed4145986c85ae5b20805"
 
+lodash.sortby@^4.7.0:
+  version "4.7.0"
+  resolved "https://registry.yarnpkg.com/lodash.sortby/-/lodash.sortby-4.7.0.tgz#edd14c824e2cc9c1e0b0a1b42bb5210516a42438"
+
 lodash.template@^3.0.0:
   version "3.6.2"
   resolved "https://registry.yarnpkg.com/lodash.template/-/lodash.template-3.6.2.tgz#f8cdecc6169a255be9098ae8b0c53d378931d14f"
@@ -3266,6 +3270,10 @@ punycode@^1.4.1:
   version "1.4.1"
   resolved "https://registry.yarnpkg.com/punycode/-/punycode-1.4.1.tgz#c0d5a63b2718800ad8e1eb0fa5269c84dd41845e"
 
+punycode@^2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/punycode/-/punycode-2.1.0.tgz#5f863edc89b96db09074bad7947bf09056ca4e7d"
+
 q@^1.4.1:
   version "1.5.1"
   resolved "https://registry.yarnpkg.com/q/-/q-1.5.1.tgz#7e32f75b41381291d04611f1bf14109ac00651d7"
@@ -3979,6 +3987,12 @@ tough-cookie@^2.3.2, tough-cookie@~2.3.0:
   dependencies:
     punycode "^1.4.1"
 
+tr46@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/tr46/-/tr46-1.0.1.tgz#a8b13fd6bfd2489519674ccde55ba3693b706d09"
+  dependencies:
+    punycode "^2.1.0"
+
 tr46@~0.0.3:
   version "0.0.3"
   resolved "https://registry.yarnpkg.com/tr46/-/tr46-0.0.3.tgz#8184fd347dac9cdc185992f3a6622e14b9d9ab6a"
@@ -4168,19 +4182,16 @@ webidl-conversions@^4.0.0:
   version "4.0.1"
   resolved "https://registry.yarnpkg.com/webidl-conversions/-/webidl-conversions-4.0.1.tgz#8015a17ab83e7e1b311638486ace81da6ce206a0"
 
+webidl-conversions@^4.0.1:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/webidl-conversions/-/webidl-conversions-4.0.2.tgz#a855980b1f0b6b359ba1d5d9fb39ae941faa63ad"
+
 whatwg-encoding@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/whatwg-encoding/-/whatwg-encoding-1.0.1.tgz#3c6c451a198ee7aec55b1ec61d0920c67801a5f4"
   dependencies:
     iconv-lite "0.4.13"
 
-whatwg-url@4.0.0:
-  version "4.0.0"
-  resolved "https://registry.yarnpkg.com/whatwg-url/-/whatwg-url-4.0.0.tgz#5be362f0b6e2f8760f7260df6e0e1df536f5479c"
-  dependencies:
-    tr46 "~0.0.3"
-    webidl-conversions "^3.0.0"
-
 whatwg-url@^4.3.0:
   version "4.7.0"
   resolved "https://registry.yarnpkg.com/whatwg-url/-/whatwg-url-4.7.0.tgz#202035ac1955b087cdd20fa8b58ded3ab1cd2af5"
@@ -4188,6 +4199,14 @@ whatwg-url@^4.3.0:
     tr46 "~0.0.3"
     webidl-conversions "^3.0.0"
 
+whatwg-url@^6.3.0:
+  version "6.3.0"
+  resolved "https://registry.yarnpkg.com/whatwg-url/-/whatwg-url-6.3.0.tgz#597ee5488371abe7922c843397ddec1ae94c048d"
+  dependencies:
+    lodash.sortby "^4.7.0"
+    tr46 "^1.0.0"
+    webidl-conversions "^4.0.1"
+
 which@^1.1.1, which@^1.2.10, which@^1.2.8, which@^1.2.9:
   version "1.2.11"
   resolved "https://registry.yarnpkg.com/which/-/which-1.2.11.tgz#c8b2eeea6b8c1659fa7c1dd4fdaabe9533dc5e8b"