Code:
/script SetAbandonQuest();
/script AbandonQuest();
If you hit this button it abandons the current quest that you have highlighted in your quest log. If you want to abandon your whole quest log just make sure all quests are open via the + sign and mash away. If you want to abandon quests by zone, close the zones that you wish to keep quests for with the - button, and then highlight your top quest and mash the button.