Breadcrumb is a firefox extension that adds breadcrumb functionality to the Address bar.
Once installed, Breadcrumb is delightfully simple to use. Simply double click any portion of a URL in the address bar to be taken to that location. For example:
http://pretend.com/something/else/index.htm
Double clicking on "something" will take you to the address:
http://pretend.com/something/
Or double clicking on pretend.com will take you to:
http://pretend.com/
That's it; thats all there is to it!