Really love this Add-on as it is easy to use and can block any script just by right clicking on your mouse button! If you wish to cancell the selection of the item to block, click anywhere on the page and move the mouse around to find which area gets highlighted in red to block.
If you make a mistake, simply go into the 'My Filters' tab in the settings and remove the most recent entry which will be number the highest being the newest addition to being blocked.
Best Addon in Firefox!