- Stealther can temporarily disable access to browsing history, cookies, download history, saved form information, disk cache and recently closed list and can also disable (temporarily) sending the ReferrerHeader (your referring website won't be available in the stats). These do not get cleared but only become unavailable wtich the click of a button.
- hideBad can be used to quickly close some tabs and delete browsing history, replace current tabs with some other tabs and can restore your original tabs.
- BetterPrivacy protects Firefox from undeletable flash cookies or DOM storage objects.
- Torbutton is a simple Firefox addon which provides a button to easily enable or disable the use of Tor. It's author claims that:
It is currently the only addon that will safely manage your Tor browsing to prevent IP address leakage, cookie leakage, and general privacy attacks.
It can also be combined with multi-proxy switching addons to provide Tor protection when the Tor proxy is selected and can be used independent of Tor for general privacy management with an auxiliary proxy such as privoxy or polip. - SwitchProxy Tool lets you switch between different proxy configurations, to protect your privacy.
- PhProxy InBasic protects the user differently than most similar addons. PhProxy InBasic acts as a server between the user and the page he is trying to view, downloading the page on it's server and then presenting it to the user so that only the server's IP is logged.
- Privacy Locker is an experimental Firefox addon so you will need an accout (you can get one for free, of course) which can be used to lock your bookmarks, Tools and histoy, clear private data and about:config and their shortcuts and only make them available after entering a password.
- Prefswitch allows you to change Firefox preferences with the click of a button. Can be used for switching between proxies and a lot more settings, from your statusbar. You can create profiles which enable or disable JavaScript, Greasemonkey, change the user-agent and a lot more options.
- Ghostery alerts you which codes a website uses (tracking codes, web bugs, ads, widgets, etc) to track your behavior. It supports (can track) 135 services and is weekly updated.
- SquiggleSR deceives search engines and does not allow websites to track your searched terms.
- FoxyProxy - I saved the best for my last addon in this list. It's author claims that:
It offers more features than SwitchProxy, ProxyButton, QuickProxy, xyzproxy, ProxyTex, TorButton, etc.
FoxyProxy is a proxy switcher which replaces Firefox's limited proxy capabilities. What's so great about it? Well, it allows you to set proxies based on URLS patterns.
You may also want to read: 10 Great Firefox Addons You May Not Have Heard Of