If the time range for clearing is set to "everything" a message should appear letting you know that the action cannot be undone. Another thing is that you are running version 9.0.1 where many security issues are present and that we are currently at version 18.0.2 and that it is suggested that you do an update. You can also make suggestions at the Suggestion Box

I use code in userChrome.css to remove all the Remove buttons and use the Delete key to remove (selected) items.

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

The customization files userChrome.css (interface) and userContent.css (websites) are located in the chrome folder in the user profile folder.

• http://kb.mozillazine.org/Editing_configuration

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

/* Remove buttons in "(Don't) Remember Passwords" window */
#removeSignon, #removeAllSignons {display:none!important}
#removeReject, #removeAllRejects {display:none!important}

/* Remove buttons in Cookies: "View Cookies" window */
/* #privacyPrefs button[label="Clear Cookies Now"]{display:none!important}*/
#CookiesDialog     button#removeCookie         {display:none!important}
#CookiesDialog     button#removeAllCookies     {display:none!important}

#PermissionsDialog button#removePermission     {display:none!important}
#PermissionsDialog button#removeAllPermissions {display:none!important}

I agree with the message about this problem, which was posted in February. I too just deleted all of my cookies by accident and there is no way I can "undo" this action. I would love a "warning" pop-up as suggested above. I am running the latest version of Firefox.