Adblock Plus Pop-up Addon extends the blocking functionality of Adblock Plus to block annoying pop-up windows that Adblock Plus is unable to stop.
By default, Adblock Plus doesn't block pop-ups that are opened on certain mouse clicks or other user events. Adblock Plus Pop-up Addon complements Adblock Plus with the pop-up blocking functionality. However, you'll need to add the pop-up URL to Adblock Plus Pop-up Addon's filters for it to work properly. This will only block the individual pop-up though. Alternatively, you can create a site rule in the addon preferences for the opener site which will block all popups. To do either, simply right clicking (or Ctrl-clicking) on the pop-up window and selecting "Block this window".
Adblock Plus Pop-up Addon is a useful add-on to extend the capabilities of the excellent Adblock Plus.