Mozilla Firefox
Click on Tools, then Options (or Edit | Preferences on Linux)
Select Privacy
In the Cookies panel, click on Show Cookies
To remove a single cookie click on the entry in the list and click on the Remove Cookie button
To remove all cookies click on the Remove All Cookies button
Google Chrome
Click on the "Tools" menu and select "Options".
Click the "Under the Bonnet" tab, locate the "Privacy" section and click the "Clear browsing data" button.
Select "Delete cookies and other site data" to delete all cookies from the list (alternatively, you can remove all cookies created within a specific time period by selecting the period you want from the dropdown list).
Select "Clear browsing history" to delete traces of which websites you've visited.
Select "Clear download history" to delete records of which files and programs you've downloaded.
Select "Empty the cache" to delete cached website pages.
You can also delete saved passwords (which log you into websites) and saved form data (such as your name and address).
Then click on the "Clear browsing data" button.
Click on the Close button when you've finished.