Firefox has a "Clean Private Data" feature that promises to clear all your web surfing tracks – everything including cookies, cache, temporary files, web addresses and stored passwords are deleted from the computer.
However if you are using the latest Firefox 3 browser, do not assume that this "Clean Private Data" command will clean your entire Firefox web history – anyone can easily discover the websites that you have visited using Firefox.
1. Press Ctrl+Shift+Del to open the Clear Private Data window in Firefox, select everything (including Browsing History) and hit OK. If you like, you may restart Firefox.
2. Everything should be cleared from Firefox in Step 1. Now lets click the drop-down in the Firefox address bar – you’ll see a long list of websites there. How come they are not deleted ?
3. There’re some more surprises here – from the bookmarks toolbar, click either the "Smart Bookmarks" or the "Places" folder and you’ll find another list that uncovers your browsing habits.
This is probably a bug that should be fixed in the future builds of Firefox 3 but until then, don’t rely on the browser if you are worried about privacy.