added first version of super-simple example

borderify/borderify.js

@@ -0,0 +1 @@
+document.body.style.border = "5px solid red";

borderify/manifest.json

@@ -0,0 +1,20 @@
+{
+
+  "manifest_version": 2,
+  "name": "Borderify",
+  "version": "1.0",
+
+  "applications": {
+    "gecko": {
+      "id": "borderify@mozilla.org"
+    }
+  },
+
+  "content_scripts": [
+    {
+      "matches": ["*://*.mozilla.org/*"],
+      "js": ["borderify.js"]
+    }
+  ]
+
+}