diff --git a/docs/2023-06-25-useful-tools.html b/docs/2023-06-25-useful-tools.html
index 6cb825d..908eab6 100644
--- a/docs/2023-06-25-useful-tools.html
+++ b/docs/2023-06-25-useful-tools.html
@@ -687,6 +687,46 @@ xcode-select --install</pre>
         >kazysmaster/gnome-shell-extension-disable-unredirect</a
       >
     </p>
+    <h3>
+      <a
+        id="user-content-firefox"
+        class="anchor"
+        aria-hidden="true"
+        href="#firefox"
+        ><span aria-hidden="true" class="octicon octicon-link"></span></a
+      >Firefox
+    </h3>
+    <p><code>about:config</code>:</p>
+    <ul>
+      <li>
+        <p>Disable unused features:</p>
+        <ul>
+          <li><code>extensions.pocket.enabled</code>: false</li>
+          <li><code>identity.fxaccounts.enabled</code>: false</li>
+          <li><code>reader.parse-on-load.enabled</code>: false</li>
+        </ul>
+      </li>
+      <li>
+        <p>Good settings:</p>
+        <ul>
+          <li><code>dom.event.clipboardevents.enabled</code>: false</li>
+          <li><code>dom.event.contextmenu.enabled</code>: false</li>
+          <li>
+            <code
+              >media.videocontrols.picture-in-picture.video-toggle.always-show</code
+            >: true
+          </li>
+          <li><code>network.IDN_show_punycode</code>: true</li>
+        </ul>
+      </li>
+      <li>
+        <p>Encrypted Client Hello (ECH):</p>
+        <ul>
+          <li><code>network.dns.echconfig.enabled</code>: true</li>
+          <li><code>network.dns.use_https_rr_as_altsvc</code>: true</li>
+        </ul>
+      </li>
+    </ul>
     <h2>
       <a
         id="user-content-thanks"
@@ -704,6 +744,30 @@ xcode-select --install</pre>
           >My list of useful command line tools</a
         >
       </li>
+      <li>
+        <a
+          href="http://www.quippd.com/firefox/wiki/useful-customizations/"
+          rel="nofollow"
+          >Useful Customizations for Firefox</a
+        >
+      </li>
+      <li>
+        <a
+          href="https://blog.mozilla.org/security/2021/01/07/encrypted-client-hello-the-future-of-esni-in-firefox/"
+          rel="nofollow"
+          >Encrypted Client Hello: the future of ESNI in Firefox</a
+        >
+      </li>
+      <li>
+        <a href="https://www.xudongz.com/blog/2017/idn-phishing/" rel="nofollow"
+          >Phishing with Unicode Domains</a
+        >
+      </li>
+      <li>
+        <a href="https://sizeof.cat/links/" rel="nofollow"
+          >https://sizeof.cat/links/</a
+        >
+      </li>
     </ul>
 
     <div>
diff --git a/posts/2023-06-25-useful-tools.md b/posts/2023-06-25-useful-tools.md
index dbb48ce..897621b 100644
--- a/posts/2023-06-25-useful-tools.md
+++ b/posts/2023-06-25-useful-tools.md
@@ -195,6 +195,31 @@ xcode-select --install
 
 Fix black screen when open game in fullscreen in external monitor with [kazysmaster/gnome-shell-extension-disable-unredirect](https://github.com/kazysmaster/gnome-shell-extension-disable-unredirect)
 
+### Firefox
+
+`about:config`:
+
+- Disable unused features:
+
+  - `extensions.pocket.enabled`: false
+  - `identity.fxaccounts.enabled`: false
+  - `reader.parse-on-load.enabled`: false
+
+- Good settings:
+
+  - `dom.event.clipboardevents.enabled`: false
+  - `dom.event.contextmenu.enabled`: false
+  - `media.videocontrols.picture-in-picture.video-toggle.always-show`: true
+  - `network.IDN_show_punycode`: true
+
+- Encrypted Client Hello (ECH):
+  - `network.dns.echconfig.enabled`: true
+  - `network.dns.use_https_rr_as_altsvc`: true
+
 ## Thanks
 
 - [My list of useful command line tools](https://boyter.org/posts/my-list-of-useful-command-line-tools/)
+- [Useful Customizations for Firefox](http://www.quippd.com/firefox/wiki/useful-customizations/)
+- [Encrypted Client Hello: the future of ESNI in Firefox](https://blog.mozilla.org/security/2021/01/07/encrypted-client-hello-the-future-of-esni-in-firefox/)
+- [Phishing with Unicode Domains](https://www.xudongz.com/blog/2017/idn-phishing/)
+- https://sizeof.cat/links/