diff --git a/files/en-us/mozilla/add-ons/webextensions/content_security_policy/index.md b/files/en-us/mozilla/add-ons/webextensions/content_security_policy/index.md
index 55cf26f3d06cf38..346ba987ee7d8bb 100644
--- a/files/en-us/mozilla/add-ons/webextensions/content_security_policy/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/content_security_policy/index.md
@@ -110,6 +110,8 @@ setTimeout("alert('Hello World!');", 500);
 const f = new Function("console.log('foo');");
 ```
 
+If an extension needs to run code that relies on `eval()`-like constructs, such as some templating libraries, it can isolate that code in a [sandboxed page](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sandbox) instead of loosening the extension's CSP.
+
 ### Inline JavaScript
 
 Under the default CSP, inline JavaScript is not executed. This disallows both JavaScript placed directly in `<script>` tags and inline event handlers, meaning that the following are not permitted:
diff --git a/files/en-us/mozilla/add-ons/webextensions/manifest.json/content_security_policy/index.md b/files/en-us/mozilla/add-ons/webextensions/manifest.json/content_security_policy/index.md
index 9de89d1f7bcc6cc..45c609cc26805fb 100644
--- a/files/en-us/mozilla/add-ons/webextensions/manifest.json/content_security_policy/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/manifest.json/content_security_policy/index.md
@@ -114,7 +114,7 @@ In Manifest V3, the `content_security_policy` key is an object that may have any
       <td><code>sandbox</code></td>
       <td><code>String</code></td>
       <td>
-        The content security policy used for sandboxed extension pages.
+        The content security policy used for the extension's <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sandbox">sandboxed pages</a>.
       </td>
     </tr>
   </tbody>
diff --git a/files/en-us/mozilla/add-ons/webextensions/manifest.json/index.md b/files/en-us/mozilla/add-ons/webextensions/manifest.json/index.md
index b684b1cd733c5a6..4513f1a593b0da9 100644
--- a/files/en-us/mozilla/add-ons/webextensions/manifest.json/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/manifest.json/index.md
@@ -51,6 +51,7 @@ These are the `manifest.json` keys; these keys are available in Manifest V2 and
 - [page_action](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/page_action) (Manifest V2 only in Chrome)
 - [permissions](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/permissions)
 - [protocol_handlers](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/protocol_handlers) (Firefox only)
+- [sandbox](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sandbox)
 - [short_name](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/short_name)
 - [sidebar_action](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sidebar_action)
 - [storage](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/storage) (Not supported in Firefox)
diff --git a/files/en-us/mozilla/add-ons/webextensions/manifest.json/sandbox/index.md b/files/en-us/mozilla/add-ons/webextensions/manifest.json/sandbox/index.md
new file mode 100644
index 000000000000000..a17265f0c368772
--- /dev/null
+++ b/files/en-us/mozilla/add-ons/webextensions/manifest.json/sandbox/index.md
@@ -0,0 +1,211 @@
+---
+title: sandbox
+slug: Mozilla/Add-ons/WebExtensions/manifest.json/sandbox
+page-type: webextension-manifest-key
+browser-compat: webextensions.manifest.sandbox
+sidebar: addonsidebar
+---
+
+<table class="fullwidth-table standard-table">
+  <tbody>
+    <tr>
+      <th scope="row">Type</th>
+      <td><code>Object</code></td>
+    </tr>
+    <tr>
+      <th scope="row">Mandatory</th>
+      <td>No</td>
+    </tr>
+    <tr>
+      <th scope="row">Manifest version</th>
+      <td>2 or higher</td>
+    </tr>
+    <tr>
+      <th scope="row">Example</th>
+      <td>
+        <pre class="brush: json">
+"sandbox": {
+ "pages": ["sandbox.html"]
+}</pre>
+      </td>
+    </tr>
+  </tbody>
+</table>
+
+Use the `sandbox` key to designate one or more of an extension's pages as **sandboxed pages**.
+
+Sandboxed pages are loaded with a unique, [opaque origin](/en-US/docs/Glossary/Origin#opaque_origin), instead of the extension's usual `moz-extension://` origin. As a result:
+
+- Sandboxed pages can't access [WebExtension APIs](/en-US/docs/Mozilla/Add-ons/WebExtensions/API). The `browser` and `chrome` global objects are not available.
+- Sandboxed pages can't access, and can't be accessed by, other pages in the extension. However, they can communicate through APIs such as {{DOMxRef("Window.postMessage()")}}.
+- Web platform APIs bound to the origin are unavailable. For examples, see the [`allow-same-origin`](/en-US/docs/Web/HTTP/Reference/Headers/Content-Security-Policy/sandbox#allow-same-origin) value of the `Content-Security-Policy: sandbox` directive.
+
+A sandboxed page can be given a more permissive [content security policy (CSP)](#content_security_policy_for_sandboxed_pages) than the rest of the extension. This includes a CSP that permits [`eval()`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval) and similar constructs that are blocked by an extension's [default content security policy](/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy#default_content_security_policy). Because a sandboxed page can't use WebExtension APIs or reach the rest of the extension directly, this can be done without weakening the security of the extension as a whole.
+
+This makes the `sandbox` key useful for including a third-party library that relies on `eval()` or `new Function()`: load the library in a sandboxed page, and use `postMessage()` to send it data from, and return results to, the rest of the extension.
+
+## Syntax
+
+`sandbox` is an object with these properties:
+
+<dl>
+  <dt><code>pages</code></dt>
+  <dd>
+    Required. An array of strings. A list of paths, relative to manifest.json, to the extension's sandboxed pages.
+  </dd>
+  <dt><code>content_security_policy</code></dt>
+  <dd>
+    Optional. A string. <strong>Manifest V2 only.</strong> The content security policy applied to the sandboxed pages. For the Manifest V3 equivalent, see the <code>sandbox</code> property of the <a href="/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy"><code>content_security_policy</code></a> key, described in <a href="#content_security_policy_for_sandboxed_pages">Content security policy for sandboxed pages</a>.
+  </dd>
+</dl>
+
+```json
+// Manifest V2
+"sandbox": {
+  "pages": ["sandbox.html"],
+  "content_security_policy": "sandbox allow-scripts; script-src 'self' 'unsafe-eval';"
+}
+```
+
+```json
+// Manifest V3
+"sandbox": {
+  "pages": ["sandbox.html"]
+}
+```
+
+## Content security policy for sandboxed pages
+
+In Manifest V3, the content security policy for sandboxed pages is set using the `sandbox` property of the [`content_security_policy`](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy) key. **This property is Manifest V3 only.** In Manifest V2, use the `content_security_policy` property of the `sandbox` key instead, as described in [Syntax](#syntax) above.
+
+```json
+"content_security_policy": {
+  "sandbox": "sandbox allow-scripts; script-src 'self' 'unsafe-eval';"
+}
+```
+
+If a policy is not supplied, sandboxed pages get this default content security policy:
+
+```plain
+sandbox allow-scripts; script-src 'self';
+```
+
+This isolates a sandboxed page from the rest of the extension, but doesn't allow `eval()` or similar constructs. To permit these, include `'unsafe-eval'` in the `script-src` directive of a custom policy.
+
+Any custom policy supplied for sandboxed pages must meet these requirements:
+
+- It must include the {{CSP("sandbox")}} directive.
+- The {{CSP("sandbox")}} directive must not include the `allow-same-origin` keyword. Allowing this would give the page access to the rest of the extension's origin, defeating the purpose of sandboxing it.
+
+## Best practices
+
+When using a sandboxed page, consider these best practices:
+
+- **Validate messages.** As a sandboxed page communicates with the rest of the extension using {{DOMxRef("Window.postMessage()")}}, it's exposed to the same risks as any other use of `postMessage()`. Check the origin and shape of every message before acting on it. See [security concerns](/en-US/docs/Web/API/Window/postMessage#security_concerns) in the `postMessage()` documentation.
+- **Don't execute untrusted code.** Although a sandboxed page can't use WebExtension APIs, its `moz-extension://` URL identifies the extension. Therefore, untrusted code running in the sandbox could be used to fingerprint the extension or its user.
+- **Don't relax the CSP only to enable WebAssembly.** If WebAssembly support is the only reason for using a sandboxed page, add `'wasm-unsafe-eval'` to the extension's [`content_security_policy`](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/content_security_policy) instead of relaxing the CSP of a sandboxed page.
+
+## Example
+
+This example loads a third-party templating library that uses `eval()`-like constructs into a sandboxed page, and uses it from a popup.
+
+`manifest.json`:
+
+```json
+{
+  "manifest_version": 3,
+  "name": "Sandbox example",
+  "version": "1.0",
+  "action": {
+    "default_popup": "popup.html"
+  },
+  "sandbox": {
+    "pages": ["sandbox.html"]
+  },
+  "content_security_policy": {
+    "sandbox": "sandbox allow-scripts; script-src 'self' 'unsafe-eval';"
+  }
+}
+```
+
+`sandbox.html`:
+
+```html
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <script src="templating-library.js"></script>
+    <script src="sandbox.js"></script>
+  </head>
+  <body></body>
+</html>
+```
+
+`templating-library.js` stands in for a third-party library that compiles templates using `new Function()`, which is why it must run in a sandboxed page:
+
+```js
+const TemplatingLibrary = {
+  compile: (template) => (context) =>
+    new Function(...Object.keys(context), `return \`${template}\`;`)(
+      ...Object.values(context),
+    ),
+};
+```
+
+`sandbox.js` listens for messages from the popup, renders a template using the sandboxed library, and posts the result back:
+
+```js
+window.addEventListener("message", (event) => {
+  if (event.source !== window.parent) {
+    // Ignore messages from any window other than the
+    // extension page that embeds this sandboxed page.
+    // The sandboxed page has an opaque origin, so
+    // location.origin can't be used for this check.
+    return;
+  }
+  const { template, context } = event.data;
+  const render = TemplatingLibrary.compile(template);
+  event.source.postMessage({ result: render(context) }, event.origin);
+});
+```
+
+`popup.html` embeds the sandboxed page in a hidden iframe. The `defer` attribute on `popup.js` ensures it only runs after the iframe has been parsed:
+
+```html
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <script src="popup.js" defer></script>
+  </head>
+  <body>
+    <iframe id="sandbox" src="sandbox.html" hidden></iframe>
+  </body>
+</html>
+```
+
+`popup.js` sends data to the sandboxed page and handles the result:
+
+```js
+const sandbox = document.getElementById("sandbox");
+
+sandbox.addEventListener("load", () => {
+  sandbox.contentWindow.postMessage(
+    { template: "Hello, ${name}!", context: { name: "world" } },
+    "*",
+  );
+});
+
+window.addEventListener("message", (event) => {
+  if (event.source !== sandbox.contentWindow) {
+    // Ignore messages from any window other than the sandboxed page.
+    return;
+  }
+  console.log(event.data.result);
+});
+```
+
+## Browser compatibility
+
+{{Compat}}
diff --git a/files/en-us/mozilla/firefox/releases/154/index.md b/files/en-us/mozilla/firefox/releases/154/index.md
index 0912beea4e0d8c2..8a14bf7648cfcfb 100644
--- a/files/en-us/mozilla/firefox/releases/154/index.md
+++ b/files/en-us/mozilla/firefox/releases/154/index.md
@@ -75,9 +75,7 @@ Firefox 154 is the current [Beta version of Firefox](https://www.firefox.com/en-
 
 ## Changes for add-on developers
 
-<!-- ### Removals -->
-
-<!-- ### Other -->
+- Adds support for the [`sandbox`](/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/sandbox) manifest key, enabling extensions to designate pages that load with an opaque origin, without direct access to extension APIs. A sandboxed page can use `eval()` and similar constructs that are otherwise blocked by the extension's [content security policy](/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_Security_Policy). ([Firefox bug 1685123](https://bugzil.la/1685123))
 
 ## Experimental web features