Locationbar² adds breadcrumbs, domain emphasis to your Firefox address bar
One worth checking out is Locationbar². You can see one of the add-on's features in my screenshot. Hold down your control, shift, or alt key and directories in the URL become clickable. While it's not useful everywhere, it does come in handy when browsing many download and shopping sites (especially those with poorly-designed navigation).
Locationbar² also adds emphasis to the current domain name. It's a good way to make sure you're not being spoofed by a deceptive link - to a fake Facebook or Hotmail login page, for example.
Head to the options screen to customize the color used and set the text to bold if you choose. While there, you can also optionally hide protocol prefixes (like http://. https://, ftp://. and file://), tweak the linkification settings, and more.