diff --git a/extensions/chromium/feature-detect.js b/extensions/chromium/feature-detect.js
deleted file mode 100644
index 91cfc90b8..000000000
--- a/extensions/chromium/feature-detect.js
+++ /dev/null
@@ -1,125 +0,0 @@
-/*
-Copyright 2014 Mozilla Foundation
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-'use strict';
-
-var Features = {
-  featureDetectLastUA: '',
-  // Whether ftp: in XMLHttpRequest is allowed
-  extensionSupportsFTP: false,
-  // Whether redirectUrl at onHeadersReceived is supported.
-  webRequestRedirectUrl: false,
-};
-
-chrome.storage.local.get(Features, function(features) {
-  Features = features;
-  if (features.featureDetectLastUA === navigator.userAgent) {
-    // Browser not upgraded, so the features did probably not change.
-    return;
-  }
-
-  // In case of a downgrade, the features must be tested again.
-  var lastVersion = /Chrome\/\d+\.0\.(\d+)/.exec(features.featureDetectLastUA);
-  lastVersion = lastVersion ? parseInt(lastVersion[1], 10) : 0;
-  var newVersion = /Chrome\/\d+\.0\.(\d+)/.exec(navigator.userAgent);
-  var isDowngrade = newVersion && parseInt(newVersion[1], 10) < lastVersion;
-
-  var inconclusiveTestCount = 0;
-
-  if (isDowngrade || !features.extensionSupportsFTP) {
-    features.extensionSupportsFTP = featureTestFTP();
-  }
-
-  if (isDowngrade || !features.webRequestRedirectUrl) {
-    ++inconclusiveTestCount;
-    // Relatively expensive (and asynchronous) test:
-    featureTestRedirectOnHeadersReceived(function(result) {
-      // result = 'yes', 'no' or 'maybe'.
-      if (result !== 'maybe') {
-        --inconclusiveTestCount;
-      }
-      features.webRequestRedirectUrl = result === 'yes';
-      checkTestCompletion();
-    });
-  }
-
-  checkTestCompletion();
-
-  function checkTestCompletion() {
-    // Only stamp the feature detection results when all tests have finished.
-    if (inconclusiveTestCount === 0) {
-      Features.featureDetectLastUA = navigator.userAgent;
-    }
-    chrome.storage.local.set(Features);
-  }
-});
-
-// Tests whether the extension can perform a FTP request.
-// Feature is supported since Chromium 35.0.1888.0 (r256810).
-function featureTestFTP() {
-  var x = new XMLHttpRequest();
-  // The URL does not need to exist, as long as the scheme is ftp:.
-  x.open('GET', 'ftp://ftp.mozilla.org/');
-  try {
-    x.send();
-    // Previous call did not throw error, so the feature is supported!
-    // Immediately abort the request so that the network is not hit at all.
-    x.abort();
-    return true;
-  } catch (e) {
-    return false;
-  }
-}
-
-// Tests whether redirectUrl at the onHeadersReceived stage is functional.
-// Feature is supported since Chromium 35.0.1911.0 (r259546).
-function featureTestRedirectOnHeadersReceived(callback) {
-  // The following URL is really going to be accessed via the network.
-  // It is the only way to feature-detect this feature, because the
-  // onHeadersReceived event is only triggered for http(s) requests.
-  var url = 'http://example.com/?feature-detect-' + chrome.runtime.id;
-  function onHeadersReceived(details) {
-    // If supported, the request is redirected.
-    // If not supported, the return value is ignored.
-    return {
-      redirectUrl: chrome.runtime.getURL('/manifest.json'),
-    };
-  }
-  chrome.webRequest.onHeadersReceived.addListener(onHeadersReceived, {
-    types: ['xmlhttprequest'],
-    urls: [url],
-  }, ['blocking']);
-
-  var x = new XMLHttpRequest();
-  x.open('get', url);
-  x.onloadend = function() {
-    chrome.webRequest.onHeadersReceived.removeListener(onHeadersReceived);
-    if (!x.responseText) {
-      // Network error? Anyway, can't tell with certainty whether the feature
-      // is supported.
-      callback('maybe');
-    } else if (/^\s*\{/.test(x.responseText)) {
-      // If the response starts with "{", assume that the redirection to the
-      // manifest file succeeded, so the feature is supported.
-      callback('yes');
-    } else {
-      // Did not get the content of manifest.json, so the redirect seems not to
-      // be followed. The feature is not supported.
-      callback('no');
-    }
-  };
-  x.send();
-}
diff --git a/extensions/chromium/pdfHandler.html b/extensions/chromium/pdfHandler.html
index 728a038c3..a87cec438 100644
--- a/extensions/chromium/pdfHandler.html
+++ b/extensions/chromium/pdfHandler.html
@@ -14,7 +14,6 @@ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 -->
-<script src="feature-detect.js"></script>
 <script src="options/migration.js"></script>
 <script src="preserve-referer.js"></script>
 <script src="pdfHandler.js"></script>
diff --git a/extensions/chromium/pdfHandler.js b/extensions/chromium/pdfHandler.js
index 5dac71546..1a6c3be5c 100644
--- a/extensions/chromium/pdfHandler.js
+++ b/extensions/chromium/pdfHandler.js
@@ -13,7 +13,6 @@ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
-/* import-globals-from feature-detect.js */
 /* import-globals-from preserve-referer.js */
 
 'use strict';
@@ -131,21 +130,7 @@ chrome.webRequest.onHeadersReceived.addListener(
     // Implemented in preserve-referer.js
     saveReferer(details);
 
-    // Replace frame with viewer
-    if (Features.webRequestRedirectUrl) {
-      return { redirectUrl: viewerUrl, };
-    }
-    // Aww.. redirectUrl is not yet supported, so we have to use a different
-    // method as fallback (Chromium <35).
-
-    if (details.frameId === 0) {
-      // Main frame. Just replace the tab and be done!
-      chrome.tabs.update(details.tabId, {
-        url: viewerUrl,
-      });
-      return { cancel: true, };
-    }
-    console.warn('Child frames are not supported in ancient Chrome builds!');
+    return { redirectUrl: viewerUrl, };
   },
   {
     urls: [
@@ -157,10 +142,6 @@ chrome.webRequest.onHeadersReceived.addListener(
 
 chrome.webRequest.onBeforeRequest.addListener(
   function onBeforeRequestForFTP(details) {
-    if (!Features.extensionSupportsFTP) {
-      chrome.webRequest.onBeforeRequest.removeListener(onBeforeRequestForFTP);
-      return;
-    }
     if (isPdfDownloadable(details)) {
       return;
     }
@@ -271,3 +252,10 @@ chrome.runtime.onMessage.addListener(function(message, sender, sendResponse) {
     }
   }
 });
+
+// Remove keys from storage that were once part of the deleted feature-detect.js
+chrome.storage.local.remove([
+  'featureDetectLastUA',
+  'webRequestRedirectUrl',
+  'extensionSupportsFTP',
+]);