To block cookies from a particular website, follow the procedure below:
- Open Firefox and go to Tools>Options>Privacy tab.
- "Use custom settings for history".
- Click on the Exceptions button,
- Copy paste the URL of the website(s) the appropriate field.
- Click on the Block button and press the Close button.
- To revert the changes simply redo the above procedure, but instead make use of the "Allow" button (the URLs you have previously added shall all be listed).