A: 

Firebug lite can be run from a bookmarklet, rather than having it load on each page.

http://getfirebug.com/firebuglite

As it's a javascript debugger, you'll only need it if you're editing js in the shell - eg SheerUI apps, custom fields etc.

adam
A: 

Firebug lite is included automatically with the Sitecore editor. Simply press F12 to bring it up within the context of the window you are working in.

It really has no benefit for the content author. As Adam said, it's main benefit is for developers working on changes to the shell.

Sean Kearney
so it can be removed because "Firebug lite can be run from a bookmarklet rather than having it load on each page"
metal-gear-solid
I don't know how easy it will be to 'remove' it from the Sitecore client nor the implications of doing so. Dare I ask why you are looking to remove it?
Sean Kearney
+1  A: 

You can safely remove the firebuglite script from the shell.

To do so, open the Core database and navigate to

/sitecore/layout/Devices/Internet Explorer

and delete the Firebug Lite item.

Jakob Christensen