Protecting from phishing, viruses, thieves and hacker you may want to consider beefing up your Firefox’s security in general. If you’re really attentive about keeping your activity on certain websites and keep hackers away from delay on your private data then this list will be great resource for you. As I mention above there are thousand of add-ons doing same task so I have mainly consider about the effective side and popularity of the add-ons that I listed here.
Note: Theses add-ons are not hosted in our server or any other particular place. I have linked directly to the Firefox add-ons page. Also when creating this list I have only consider only about add-ons those are compatible with Firefox3. 
- Cookies can mess-up
CookieSafeThis extension will allow you to easily control cookie permissions. It will appear on your statusbar. Just click on the icon to allow, block, or temporarily allow the site to set cookies.
View CookiesIt adds a tab to the Page Info dialog box, which shows the cookies belonging to the current page.
Add N Edit CookiesCookie Editor that allows you add and edit "session" and saved.
CookieSwap CookieSwap enables you to easily swap all your cookies so that you can be logged in to multiple web e-mail accounts (like Gmail and Yahoo! mail) at the same time and quickly switch between them.
Cookie MonsterTemporary Permission for sites to leave cookies, Set general Firefox setting to block all cookies -Updated menu structure, view cookies for current site or all sites, A panel for indicating the current status of cookies, Cookie Monster allows for easier managing of what sites a user allows to set cookies and what sites cannot. It works best for users who do NOT accept cookies by default, although this is not necessary.
CookieCullerDelete unwanted cookies
- Encrypting data is the best way to hide secret reserves
Gmail S/MIMESend and receive signed and encrypted messages in Gmail.
KeyScrambler PersonalKeyScrambler Personal encrypts your keystrokes at the kernel driver level to protect your information from keyloggers. (Windows only)
- Protect your Secrecy
StealtherThis add-on can temporarily disable the Browsing History (also in Address bar), Cookies, Downloaded Files History, Disk Cache, Saved Form Information, Sending of Referrer Header, Recently Closed Tabs list
SecureBrowseThis is a security extension for Firefox that takes care of clearing private data (cookies, saved passwords, form history etc)
Secure LoginSecure Login is a login extension for Mozilla Firefox integrated password manager. Its main feature is similar to Opera's (the browser) Wand login.
FormFoxThis extension displays the form action (the site to which the information you've entered is being sent.) personally I love this extension. This can use to grab information from any web site.
HideBadQuickly closes tabs that you do not want others to see. Also clears your history and such at your discretion.
GhostfoxMove your mouse away and Firefox disappears. Then sweep it from the left edge of the screen, back to the right edge and again to the left edge. (Windows only)
- Check every aspects of web sites can Beef up system Security
Dr.Web anti-virus link checkerThis allows you to check any file you are about to download, any page you are about to visit with online version of Dr.Web anti-virus
No-RefererAllow you to open a link without sending the HTTP referrer header.
InterclueEver wanted to know what was behind the link before you clicked? Interclue tells you everything you need to know before you open yet another tab.
JSViewJsview can use to view the source code of external files of any web site.
Finjan SecureBrowsingFinjan SecureBrowsing is a free service that proactively alerts you to potential malicious content hiding behind links of search results, ads and other selected web pages.
BlockSiteBlockSite is an extension, which automatically blocks websites of your choice.
Cert Viewer PlusCertificate viewer enhancements: PEM format view, file export
EnigformOpen PGP Enhancements to HTTP. Implement Secure Session Management (user/password-less login to mod_openpgp enabled Apache web servers) and Signed Requests.
- Keep away phishing sites is best for prevent data leaks
PhishTank SiteCheckerPhishTank SiteChecker gives Firefox users a way to bring the community judgment of PhishTank
Netcraft ToolbarBlocks phishing sites, helping to protect users from online fraud
WOTWOT, Web of Trust, warns you about risky websites that try to scam visitors, deliver malware or send spam.
- Using disposal mail accounts is best for spamming
Spamavert.comGenerates temporary e-mail addresses for all those pesky online registration forms using the free spamavert.com
TrashMail.netCreate free disposable email addresses and paste them directly in forms.
TempomailCreate temporary email addresses to prevent your mailbox from
- Hide Identity with Proxies
External IPThis extension displays your current external IP address in the browsers status bar. (This extension can use to check either proxies are working or not, so I have decided to itemize this extension with proxy section)
gladderA proxy tool works on a customizable sites list!
QuickProxyStatus bar button to turn the proxy on and off with a single click.
PhProxy - InBasicFirefox add-on to achieve anonymity in surfing, using web-based proxy
Tor-Proxy.NET ToolbarGet Safety and Anonymity by using TOR-Proxy.NET for surfing! Tor-Proxy.NET is a CGI-Web-Proxy, which tunnels your traffic through different anonymization -networks.
TorbuttonTorbutton provides a button to securely and easily enable or disable the browser's use of Tor. It is currently the only add-on that will safely manage your Tor browsing to prevent IP address leakage, cookie leakage, and general privacy attacks
SwitchProxy ToolSwitch Proxy lets you manage and switch between multiple proxy configurations
- Passwords
SecurePassword GeneratorHelps you create truly unique and secure passwords.
Master Password TimeoutLock the master security device after a predefined period of inactivity to prevent unauthorized use of saved passwords.
Secure LoginSecure Login is a login extension for Mozilla Firefox integrated password manager. Its main feature is similar to Opera's (the browser) Wand login.
PasswordMakerOne Password To Rule Them All!
Password HasherBetter security without bursting your brain
PwdHashAutomatically generates per-site passwords if you prefix your password with @@ or press F2 beforehand. Prevent Java Scripts from reading your password as it is typed.
Password ExporterThis extension allows you to export your saved passwords and disabled login hosts using XML or CSV files that can be imported in another browser or computer.
BugMeNotBypass compulsory web registration with the context menu via www.bugmenot.com
- Your Privacy can expose to others if they remaining
Clear Private DataThis extension makes Firefox' "Clear Private Data..." feature more accessible.
Page Title EraserThe Page Title Eraser (PTE) is a simple Mozilla Firefox extension which allows hiding title and icon (favicon.ico) of the selected tab. It provides more privacy at your workplace. (Windows only)
DistrustHide surfing trails that the browser leaves behind (Turn on this app when you start surfing the Web. Turn it off when you’re finished, and all of your history will delete)
SecureBrowsesecurity extension for Firefox that takes care of clearing private data (cookies, saved passwords, form history etc) when necessary.
SquiggleSR Deceive search engines to protect user privacy. Queries are generated using personalized keywords and clicks are randomly simulated on non-sponsored results.
TabRenamizerever you noticed that everybody looks the titles of your open tabs? It has a name: Paranoia! And a solution too: TabRenamizer!
TrackMeNotProtects users against search data profiling
- Some java scripts can malicious
Controle de ScriptsControle de Scripts is an extension that allows you to control what JavaScripts do on your browser.
NoScriptThe best security you can get in a web browser! Allow active content to run only from sites you trust, and protect your self against XSS attacks.
JavaScript OptionsProvides advanced JavaScript options for Firefox.
