import and export based on http://add0n.com/useragent-switcher.html#IDComment1079854533

extension/data/options/index.html

@@ -70,6 +70,11 @@
       <td><textarea id="protected" rows="3" wrap="off"></textarea></td>
     </tr>
   </table>
+
+  <p>
+    <button id="import">Import Settings</button>
+    <button id="export">Export Settings</button>
+  </p>
   <p>
     <button id="help">FAQs Page (Help)</button>
     <button id="donate">Support Development</button>

extension/data/options/index.js

@@ -135,3 +135,53 @@ document.getElementById('help').addEventListener('click', () => {
     url: chrome.runtime.getManifest().homepage_url
   });
 });
+
+// export
+document.getElementById('export').addEventListener('click', () => {
+  chrome.storage.local.get(null, prefs => {
+    const text = JSON.stringify(prefs, null, '  ');
+    const blob = new Blob([text], {type: 'application/json'});
+    const objectURL = URL.createObjectURL(blob);
+    Object.assign(document.createElement('a'), {
+      href: objectURL,
+      type: 'application/json',
+      download: 'useragent-switcher-preferences.json'
+    }).dispatchEvent(new MouseEvent('click'));
+    setTimeout(() => URL.revokeObjectURL(objectURL));
+  });
+});
+// import
+document.getElementById('import').addEventListener('click', () => {
+  const input = document.createElement('input');
+  input.style.display = 'none';
+  input.type = 'file';
+  input.accept = '.json';
+  input.acceptCharset = 'utf-8';
+
+  document.body.appendChild(input);
+  input.initialValue = input.value;
+  input.onchange = readFile;
+  input.click();
+
+  function readFile() {
+    if (input.value !== input.initialValue) {
+      const file = input.files[0];
+      if (file.size > 100e6) {
+        console.warn('100MB backup? I don\'t believe you.');
+        return;
+      }
+      const reader = new FileReader();
+      reader.onloadend = event => {
+        input.remove();
+        const json = JSON.parse(event.target.result);
+        chrome.storage.local.clear(() => {
+          chrome.storage.local.set(json, () => {
+            window.close();
+            chrome.runtime.reload();
+          });
+        });
+      };
+      reader.readAsText(file, 'utf-8');
+    }
+  }
+});

extension/data/popup/index.html

@@ -78,7 +78,7 @@
           <td>userAgent</td>
           <td colspan="3">
             <div hbox>
-              <input id="ua" type="text" placeholder="Your preferred user-agent string" title="To set blank user-agent string, use 'empty' keyword">
+              <input id="ua" type="text" placeholder="Your preferred user-agent string" title="To set a blank user-agent string, use the 'empty' keyword. To construct a custom user-agent string based on the current browser's navigator object, use ${} notation. Whatever is inside this notation is read from the 'navigator' object. For instance, to append a string to the default user-agent, use '${userAgent} THIS IS THE APPENDED STRING'">
             </div>
           </td>
         </tr>