Cookies are a way for websites and services to store information on your computer and they are small files that are saved to the disk drive as you browse the web. Some cookies are very useful, such as those that store usernames to aid logins, website preferences, shopping carts and so on.
Not all cookies are useful though and they can be used to track where you have been and what you have looked at on the web. Advertisers use them to record the sites adverts were viewed on, which adverts were viewed and other information.
Self-Destructing cookies is an add-on for Firefox that enables you to automatically erase the cookies you don't need while keeping the ones that are useful.
If you tried to browse the web with cookies disabled, you would find that some sites don't work or that features are limited, but when cookies are enabled anyone can store information about you in them. Neither extreme is particularly desirable, so Self-Destructing Cookies allows you to browse the web with cookies enabled, but they are automatically erased when you close the browser window or just a tab. It is a clever and useful add-on.
To install it, go to the Firefox menu and select Add-ons. In the search box at the top, enter self destructing cookies (here's a direct link if you can't find it). When this add-on is installed, it starts with a clean slate, so be aware that it will delete all existing cookies. It displays a help screen immediately after installation and by clicking the button in the browser's toolbar you can undelete the cookies if you want. It is best to erase them and start afresh, but be aware that you will lose any website login details and preferences for some sites. Make sure you know your usernames and passwords!
If you don't see the button in toolbar at the top of window, go to the Firefox menu and select Add-ons. Select Extensions and make sure Self Destructing Cookies is enabled.
When you visit a website, click the button in the toolbar. There are options to self-destruct the site's cookies when the tab is closed, the browser is closed, or never. Choose never for sites that store useful information like login details, shopping, forums perhaps, and so on. Choose one of the close options for unimportant sites that you don't shop, bank, or do anything else useful.
There are a number of useful options, such as a timer, whitelist and statistics. Go to the Firefox menu and select Addons. Select Extensions and click Options under Self-Destructing Cookies. There is a grace period and you can set a timer so that cookies are removed if unused for a certain period of time. Ten seconds is the default. Cookies can be deleted if the browser is idle for a certain length of time too. You can choose whether to see notifications.
Down at the bottom is Whitelist. Click the Edit Whitelist button and you can add websites where Self-Destructing Cookies is disabled.
Enter the URL without the www. at the start. This allows all web pages that are on the site to create and access cookies. Any site where cookies are essential should be added and there are probably a few you will find useful, like online banking and other places you log into.