Firebug for firefox is okay. The console for safari and chrome, IMO, is better. In either case, right click the page, hit "inspect element," and click the "console" tab in the pane that pops up. Now you'll see any errors and warnings generated by the page.
If you really want to debug the scripts you can click on the "Scripts" tab and either pause execution immediately or set a break point. Then, you can step through the execution of the script line by line, inspecting the call stack and watch list as you go.
