I found some of these plugins are very useful.
Developers Addons
1) Firebug – Edit monitor, inspect CSS
2) Web Developer toolbar
3) Html Validator to validate HTML syntax
4) JavaScript Debugger – Editor for Javascript
5) FireFTP
6) Aardvark – To view CSS attributes, id, class by highlighting page element
individually.
7) Screen grab – Capture screenshot of any webpage and save it.
NoScript – click once to bloack and unblock java and javascript.
9) Image Zoom
10) Clear cache button – click once to clear the cache
11) JSView show all external javascript files
