Bump supported version of FF to 3

2 doesn't have getBoundingClientRect, which we use extensively.

Closes #1062

Author: marijnh

index.html

@@ -215,7 +215,7 @@ <h2 id="supported">Supported browsers</h2>
   <p>The following <em>desktop</em> browsers are able to run CodeMirror:</p>
 
   <ul>
-    <li>Firefox 2 or higher</li>
+    <li>Firefox 3 or higher</li>
     <li>Chrome, any version</li>
     <li>Safari 5.2 or higher</li>
     <li>Opera 9 or higher (with some key-handling problems on OS X)</li>