diff --git a/open-my-page-button/README.md b/open-my-page-button/README.md
index bfb9033..1f4bbe9 100644
--- a/open-my-page-button/README.md
+++ b/open-my-page-button/README.md
@@ -1,5 +1,7 @@
 # open-my-page
 
+## What it does
+
 This extension includes:
 
 * a background script, "background.js"
@@ -8,7 +10,7 @@ This extension includes:
 
 All it does is: when the user clicks the button, open "my-page.html" in a new tab.
 
-It shows:
+## What it shows
 
 * how to listen for browser action clicks in a background script
 * how to open a page packaged with your extension
diff --git a/page-to-extension-messaging/README.md b/page-to-extension-messaging/README.md
new file mode 100644
index 0000000..e1c7761
--- /dev/null
+++ b/page-to-extension-messaging/README.md
@@ -0,0 +1,15 @@
+# page-to-extension-messaging
+
+## What it does
+
+This extension includes a content script, which is injected only into: "https://mdn.github.io/webextensions-examples/content-script-page-script-messaging.html".
+
+The content script listens for clicks on a particular button on the page. When the button is clicked, the content script sends a message to any scripts running in the page.
+
+Conversely, the content script listens for messages from the same window posted using window.postMessage. When the content script receives such a message, it displays an alert.
+
+To test it out, visit https://mdn.github.io/webextensions-examples/content-script-page-script-messaging.html and press the buttons. One button sends a message from the page script to the content script, the other button sends a message in the other direction.
+
+## What it shows
+
+How to exchange messages between an extension's content scripts, and scripts running in a web page.
diff --git a/tabs-tabs-tabs/README.md b/tabs-tabs-tabs/README.md
index 9bacd34..43d3cb5 100644
--- a/tabs-tabs-tabs/README.md
+++ b/tabs-tabs-tabs/README.md
@@ -1,8 +1,11 @@
 # tabs, tabs, tabs
 
-This extension includes:
+## What it does
 
-* a browser action
-* a page "tabs.html" with a script "tabs.js"
+This extension includes a browser action with a popup specified as "tabs.html".
 
-It shows a list of tab methods that you can perform on the active tab.
+The popup lets the user perform various simple operations using the tabs API.
+
+# What it shows
+
+Demonstration of various tabs API functions.
diff --git a/user-agent-rewriter/README.md b/user-agent-rewriter/README.md
new file mode 100644
index 0000000..de0bd80
--- /dev/null
+++ b/user-agent-rewriter/README.md
@@ -0,0 +1,14 @@
+# user-agent-rewriter
+
+## What it does
+
+This extension uses the webRequest API to rewrite the browser's User Agent header, but only when visiting pages under "http://useragentstring.com/".
+
+It adds a browser action. The browser action has a popup that lets the user choose one of three browsers: Firefox 41, Chrome 41, and IE 11. When the user chooses a browser, the extension then rewrites the User Agent header so the real browser identifies itself as the chosen browser on the site http://useragentstring.com/.
+
+## What it shows
+
+* how to intercept and modify HTTP requests
+* how to write a browser action with a popup
+* how to give the popup style and behavior using CSS and JS
+* how to send a message from a popup script to a background script