The Remove All Cookies extension for Firefox installs a new button in the Firefox toolbar. If you want to remove the cookies related to a website then first you have to open that website in Firefox and then click on this new button in the toolbar. All of the cookies stored from that website in Firefox are instantly cleaned without any warning.
You can also right-click anywhere on the web page of that website and choose to Remove Cookies for Site from the right-click context menu. Again, there is no alert, warning or prompt before the cookies belonging to that website get removed. However, this extension removes the cookies belonging to the website currently open in the selected tab of Firefox. It does not clean any third party websites.
Conclusion: The Remove All Cookies extension for Firefox can be helpful for surfing the web without revealing your earlier online activities as the cookies for a website can be instantly cleaned in a single-click.
You can download the Remove All Cookies extension for Firefox from https://addons.mozilla.org/en-US/firefox/addon/remove-cookies-for-site/.