When you are working on a project involved with lot of scripts.In firebug under script tag you have an option of searching for a js file in the suggestion box provided.
Where as with chrome you will have a lame tree view to locate your JS file which is tedious to see the namespacing of your js file and traverse the tree.
This option might not affect anyone who involves with little JS files in their project. This feature is a bang on with firebug I use when my scripts are more than 1000 JS files.