Here is a list of very cool firefox addons which I think every serious Network/SysAdmin should have in his/her toolbox ;-)
- httpfox https://addons.mozilla.org/en-US/firefox/addon/6647 2. Tamper data https://addons.mozilla.org/en-US/firefox/addon/966
- Live http header https://addons.mozilla.org/en-US/firefox/addon/3829
- Nagios Checker https://addons.mozilla.org/en-US/firefox/addon/3607
- Asnumber https://addons.mozilla.org/en-US/firefox/addon/2072
- Cisco Doc Search Plugin https://addons.mozilla.org/en-US/firefox/addon/11390
- Modify Headers https://addons.mozilla.org/en-US/firefox/addon/967
Feel free to add any other extension you think could be an invaluable tool in the day to day job.