diff --git a/lighthouse-cli/performance-experiment/report/partials/config-panel.html b/lighthouse-cli/performance-experiment/report/partials/config-panel.html
index 5207c071c52b..51e2e749ca17 100644
--- a/lighthouse-cli/performance-experiment/report/partials/config-panel.html
+++ b/lighthouse-cli/performance-experiment/report/partials/config-panel.html
@@ -114,6 +114,7 @@
   transform: translate(0px, 5px);
   border: none;
   flex: 0 0 auto;
+  vertical-align: top;
   background-repeat: no-repeat;
   background-position: center center;
   background-size: 16px 16px;
diff --git a/lighthouse-cli/performance-experiment/report/scripts/perf-x.js b/lighthouse-cli/performance-experiment/report/scripts/perf-x.js
index a4262a14dcca..f46972e3202d 100644
--- a/lighthouse-cli/performance-experiment/report/scripts/perf-x.js
+++ b/lighthouse-cli/performance-experiment/report/scripts/perf-x.js
@@ -31,7 +31,8 @@ class ConfigPanel {
     this._messageField = this._configPanel.querySelector('.js-message');
     this._urlBlockingList = this._configPanel.querySelector('.js-url-blocking-patterns');
     this._urlBlockingStatus = {};
-    this._reportId = new URL(window.location).searchParams.get('id');
+    const match = location.search.match(/[?&]id=([^&]*)/);
+    this._reportId = match ? match[1]: '';
 
     const bodyToggle = this._configPanel.querySelector('.js-panel-toggle');
     bodyToggle.addEventListener('click', () => this._toggleBody());
@@ -83,15 +84,6 @@ class ConfigPanel {
         }
       });
     });
-
-    // get and recover blocked URL patterns of current run
-    fetch(`/flags?id=${this._reportId}`).then(response => {
-      return response.json();
-    }).then(flags => {
-      const blockedUrlPatterns = flags.blockedUrlPatterns || [];
-      blockedUrlPatterns.forEach(urlPattern => this.addBlockedUrlPattern(urlPattern));
-      this.log('');
-    });
   }
 
   /**
@@ -100,15 +92,24 @@ class ConfigPanel {
    */
   _rerunLighthouse() {
     this.log('Start Rerunning Lighthouse');
-
     const options = {
       blockedUrlPatterns: this.getBlockedUrlPatterns()
     };
 
-    return fetch(`/rerun?id=${this._reportId}`, {method: 'POST', body: JSON.stringify(options)})
-      .then(response => response.text())
-      .then(newReportId => location.assign(`?id=${newReportId}`))
-      .catch(err => this.log(`Lighthouse Runtime Error: ${err}`));
+    const xhr = new XMLHttpRequest();
+    xhr.open('POST', `/rerun?id=${this._reportId}`, true);
+    xhr.onreadystatechange = () => {
+      if (xhr.readyState !== 4) {
+        return;
+      }
+
+      if (xhr.status === 200) {
+        location.assign(`?id=${xhr.responseText}`);
+      } else if (xhr.status === 500) {
+        this.log('Error: Lighthouse runtime error');
+      }
+    };
+    xhr.send(JSON.stringify(options));
   }
 
   /**
@@ -118,8 +119,12 @@ class ConfigPanel {
    * @param {string} urlPattern
    */
   addBlockedUrlPattern(urlPattern) {
-    if (this._urlBlockingStatus[urlPattern]) {
-      this.log(`${urlPattern} is already in the list`);
+    urlPattern = urlPattern.trim();
+    if (urlPattern.length === 0) {
+      this.log('Error: URL blocking pattern is an empty string');
+      return;
+    } else if (this._urlBlockingStatus[urlPattern]) {
+      this.log(`Error: ${urlPattern} is already in the list`);
       return;
     }
 
@@ -150,8 +155,9 @@ class ConfigPanel {
    * @param {string} urlPattern
    */
   removeBlockedUrlPattern(urlPattern) {
+    urlPattern = urlPattern.trim();
     if (!this._urlBlockingStatus[urlPattern]) {
-      this.log(`${urlPattern} is not in the list`);
+      this.log(`Error: ${urlPattern} is not in the list`);
       return;
     }
 
@@ -193,5 +199,11 @@ class ConfigPanel {
 }
 
 window.addEventListener('DOMContentLoaded', () => {
-  new ConfigPanel();
+  const configPanel = new ConfigPanel();
+
+  // init recover blocked URL patterns
+  [...document.querySelectorAll('.js-currently-blocked-url')].forEach(ele => {
+    configPanel.addBlockedUrlPattern(ele.getAttribute('data-url-pattern'));
+  });
+  configPanel.log('');
 });
diff --git a/lighthouse-cli/performance-experiment/server.js b/lighthouse-cli/performance-experiment/server.js
index 2343d2a5dc6b..2e9ed311573f 100644
--- a/lighthouse-cli/performance-experiment/server.js
+++ b/lighthouse-cli/performance-experiment/server.js
@@ -25,7 +25,6 @@
  *    Browser can request lighthousr rerun by sending POST request to URL: /rerun?id=[REPORT_ID]
  *      This will rerun lighthouse with additional cli-flags received from POST request data and
  *      return the new report id
- *    Flags can be access via URL: /flags?id=[REPORT_ID]
  */
 
 const http = require('http');
@@ -69,8 +68,6 @@ function requestHandler(request, response) {
     if (request.method === 'GET') {
       if (pathname === '/') {
         reportRequestHandler(request, response);
-      } else if (pathname === '/flags') {
-        flagsRequestHandler(request, response);
       } else {
         throw new HTTPError(404);
       }
@@ -118,15 +115,6 @@ function reportRequestHandler(request, response) {
   }
 }
 
-function flagsRequestHandler(request, response) {
-  try {
-    response.writeHead(200, {'Content-Type': 'text/json'});
-    response.end(JSON.stringify(database.getFlags(request.parsedUrl.query.id || fallbackReportId)));
-  } catch (err) {
-    throw new HTTPError(404);
-  }
-}
-
 function rerunRequestHandler(request, response) {
   try {
     const flags = database.getFlags(request.parsedUrl.query.id || fallbackReportId);
@@ -142,6 +130,10 @@ function rerunRequestHandler(request, response) {
         const id = database.saveData(flags, results);
         response.writeHead(200);
         response.end(id);
+      }).catch(err => {
+        log.error('PerformanceXServer', err.code, err);
+        response.writeHead(500);
+        response.end(http.STATUS_CODES[500]);
       });
     });
   } catch (err) {
diff --git a/lighthouse-core/report/styles/report.css b/lighthouse-core/report/styles/report.css
index e074b4e70b22..c31111fcec33 100644
--- a/lighthouse-core/report/styles/report.css
+++ b/lighthouse-core/report/styles/report.css
@@ -433,6 +433,7 @@ body {
   display: none;
   padding: 10px 0 10px 42px;
   top: 100%;
+  left: 0;
   position: absolute;
   width: 100%;
   background: inherit;
diff --git a/lighthouse-core/report/templates/report-template.html b/lighthouse-core/report/templates/report-template.html
index edff114059d1..703acb73a9d6 100644
--- a/lighthouse-core/report/templates/report-template.html
+++ b/lighthouse-core/report/templates/report-template.html
@@ -108,7 +108,7 @@ <h2 class="config-section__title">Runtime Environment</h2>
               <h2 class="config-section__title">Blocked URL Patterns</h2>
               <ul class="config-section__items">
                 {{#each runtimeConfig.blockedUrlPatterns }}
-                <li class="config-section__item">
+                <li class="config-section__item js-currently-blocked-url" data-url-pattern="{{ this }}">
                   <p class="config-section__desc">{{ this }}</p>
                 </li>
                 {{/each}}