To run OpenLayers in debug mode, include the following script tag before the tag that loads OpenLayers:
<script src="../lib/Firebug/firebug.js"></script>
The path to firebug.js must be relative to your
html file. With this script included calls to OpenLayers.Console
will be displayed in the Firebug console. For browsers without
the Firebug extension, the script creates a Firebug Lite console.
This console can be opened by hitting F12 or Ctrl+Shift+L
(?+Shift+L on a Mac). If you want the Firebug Lite console
to be open when the page loads, add debug="true" to the opening
html tag of your page. Open the console and click on the links below
to see console calls.
The Firebug website has a complete list of console calls. Note that not all are supported with Firebug Lite.