If you want to delete all Facebook message then you have to delete single single messages because Facebook won’t provide a way to select all message and delete all of them at once. In any condition if you want to delete all Facebook message and make Facebook Inbox zero then you have to put lots of effort and vary irritating if you have lots of messages.
Since it is related to script and executing script for a basic computer user may be difficult process. So i am trying to simplify the whole process . You may know that script can be executed from bookmark bar of browser so it become easy to execute for basic user and it will work in all browser in similar way. Follow the Bellow guide to delete all Facebook messages.
Step to delete all messages on Facebook
Video Tutorial To Delete All Facebook Messages.
Source and script is created by Mikisoft. You can find original script on there website.Update : 23 Feb 2013 now script is working properly. Thank you Alex to fixing and providing working Script. Here is Link to working script which is provided by Alex http://pastebin.com/nwjkSXDw .Related : Create an RSS feed notification for Facebook notification .