Firebug and Errors
Firebug Start Button
Click the red error number to open the Firebug error console which will show you all of the errors that have occurred on the page.
No error soup
Most browsers report errors by dumping them all into one big window that includes the problems with every web page you've ever visited. Firebug is kinder than that; it shows you only the errors for the page that you're looking at.
Jump to the debugger
Some errors also include the actual snippet of source that contains the error, which is also a link to the original file.
Using the quick search box, you can filter the Firebug Console to show only the errors and messages that match the text that you searched for. As new rows are added to the console, they will only appear if they match the text in the quick search box.