Below are 10 important addon for the "convenience" in making your surfing activity:
1. Adblock Plus
A large ad on a web page, in addition to "disrupt" the process will also slow loading web pages. With this addon you can block ads, both text ads and image ads (banner).
2. Flashblock
Used to block flash. Suitable for you to use the low speed internet connection. You can still play the flash terblok by pressing the Play button.
3. Scobe Tab
To display the preview of the web pages, similar to the features previewnya Opera.
4. Screengrab
With this addon you can make screenshoot display web pages.
With this addon you can download videos from hundreds of video sites on the Internet such as Youtube, Metacafe, Google Video, Yahoo Video, etc. directly from Firefox, download manager without special assistance.
6. Foxmarks
With this addon you can synchronize bookmarks (list of sites that are saved as a favorite). Suitable for your normal internet access from many places, such as office, home, cafe, etc..
7. GreaseMonkey
With GreaseMoney and the script is in the userscripts.org you can "to customize" a site, for example, by pass Rapidshare download countdown, to block the ads on GMail, create dropdown Gmail login page, etc..
8. FlashGot
This is a firefox addon that integrate with your favorite download manager. You can "combine" FlashGot with FlashGet, BitComet, Download Accelerator Plus, GetRight, MassDownloader, and so forth.
9. Tab Mix Plus 
This Addon will add many new features mainly related to the tab, for example, create a duplicate tab, lock tab, the focus, restore the closed tab, etc..
10. Fast Dial
Fast Dial will "replace" tab fill in the blank when opening new tab with the tab that contains a thumbnail of your favorite sites.
