Cool Firefox address bar tricks:

• about:?
• about:credits
• about:mozilla
• about:cache
  - about:cache?device=disk
• about:config
  - network.http.pipelining
  - network.http.pipelining.maxrequests
• chrome://global/content/MPL-1.1.html
• resource:/browserconfig.properties
• about:plugins
• about:buildconfig
• about:bloat

More info here: about:config entries, preferences, and list and guide.