You can click on the arrow of the Adblock Plus icon in the toolbar to bring up the menu. There you have the option to disable/reenable Adblock Plus. If this isn’t fast enough, simply press the middle mouse button on this icon, it will also disable or reenable Adblock Plus.
In the menu you also have the option to disable Adblock Plus on a certain page. It will add an exception rule like @@|
http://adblockplus.mozdev.org/ to your list of filters.