IMHO, these are my recommended add-on for firefox
1. ColorfulTabs, Colors every tab in a different color and makes them easy to distinguish while beautifying the overall appearance of the interface
2. Flagfox, Displays a country flag depicting the location of the current website’s server and provides quick access to detailed location and webserver information
3. Adblock Plus, Ever been annoyed by all those ads and banners on the internet that often take longer to download than everything else on the page? Install Adblock Plus now and get rid of them
4. Sothink Web Video Downloader, A simple, clean and easy-to-use FREE Firefox extension for video download and Flash download
5. Fasterfox Lite, Performance and network tweaks for Firefox, without the Prefetching.
If anyone have other opinions, please share….