If for some reason you need to browse the Internet anonymously without leaving any trace like cookies, downloaded web files, disk cache, closed tabs list etc.then there is a Firefox plugin to do that. also Google Chrome has a built-in feature called incognito to browse the web anonymously, but lets talk about the Firefox plug-in first.

Stealther is a Firefox plugin that let you browse the web anonymously in that way once you close the browser no history of your online visits is saved on the local disk of the computer. this is a good plugin to use when using a public computer, or a computer you don’t want to leave any traces on. download the plugin from Firefox addons at https://addons.mozilla.org/en-US/firefox/addon/1306 and install it. the installation is very simple. once you restart Firefox, the plugin will show up under the Tools menu on your Firefox browser:

stealther plugin

Once you click on the Stealther, Firefox will go into stealth mode. while on stealth mode, you won’t be able to login to online accounts that require to install tracking cookies, etc.
You can also choose what to disable or allow on the plugin by going to the extensions options. click on Tools, then choose Add-ons  look for the Stealther plugin and click on Options:

Firefox Entensions

the Stealther options window will pop-up:

stealther options

from here you can choose what to disable or allow by checking or unchecking the options.

Now if for some reason you don’t want to use this plugin on Firefox, then download Google Chrome. in Google Chrome you don’t need any plugin just download it, and from the menu click on the wrench icon and click on New Incognito Window:

google chrome incognito window

that should pop-up a new window totally anonymous on your browser.