When you mix simple and Firefox together, you can get my attention every time. The Simple Links Counter add-on for Firefox shows the number of internal and external links on any given page in the browser status bar. This makes it the perfect companion for all your other web developer tools and add-ons for Firefox.
By default, it gives you a simple numerical count, as seen here:
However, when you expand it, you get much more information about each link:
This comes in really handy when your looking to see how many links you have on your web site, and then see how many are external compared to internal (linking to somebody else versus linking to your own pages inside your web site).
You can pickup the Simple Links Counter for Firefox at the Firefox Add-ons web site.