Here are some useful add-ons for your Mozilla Firefox.

1.)Adblock Plus https://addons.mozilla.org/en-US/firefox/addon/1865
2.)Firefox Showcase https://addons.mozilla.org/en-US/firefox/addon/1810
3.)Foxmarks Bookmark Synchronizer https://addons.mozilla.org/en-US/firefox/addon/2410
4.)CookieCuller https://addons.mozilla.org/en-US/firefox/addon/82 Extended Cookie Manager
5.)CustomizeGoogle https://addons.mozilla.org/en-US/firefox/addon/743 Enhance Google search results by adding or removing information
Automatically synchronize multiple computers
6.)Fullerscreen https://addons.mozilla.org/en-US/firefox/addon/4650 Truly full screen

7.)GButts https://addons.mozilla.org/en-US/firefox/addon/3576 Display all of your Google Services as buttons
8.)GMail Manager https://addons.mozilla.org/en-US/firefox/addon/1320
9.)McAfee SiteAdvisor http://www.siteadvisor.com/download/ff.html
10.)Restart Firefox https://addons.mozilla.org/en-US/firefox/addon/1249
11.)Screengrab! https://addons.mozilla.org/en-US/firefox/addon/1146 Captures entire web pages no matter how long they are
12.)Session Manager https://addons.mozilla.org/en-US/firefox/addon/2324 Saves and restores the state of all windows/tabs
13.)StumbleUpon https://addons.mozilla.org/en-US/firefox/addon/138
14.)Tab Mix Plus https://addons.mozilla.org/en-US/firefox/addon/1122
15.)Toolbar Buttons https://addons.mozilla.org/en-US/firefox/addon/2377 There are now 95 buttons for Firefox, 58 for Thunderbird, and 26 for Sunbird
16.)Translator https://addons.mozilla.org/en-US/firefox/addon/3361
17.)WHOIS https://addons.mozilla.org/en-US/firefox/addon/603
18.)Google Bookmarks Button https://addons.mozilla.org/en-US/firefox/addon/2453
19.)IE Tab https://addons.mozilla.org/en-US/firefox/addon/1419
20.)Yahoo! Mail Notifier https://addons.mozilla.org/en-US/firefox/addon/1264
21.)Page hacker 1.2 https://addons.mozilla.org/en-US/firefox/addon/5753
22.)Find in Frame Hack https://addons.mozilla.org/en-US/firefox/addon/1075