Log in your facebook account, go in message section and then delete up to 1000 messages in a single click.
This version is compatible with last facebook version (messenger).
Once installed, it will simply add another button to the far right of your Facebook messages. Pressing the button will provide the possibility to delete 10 messages, 100 messages or even 1000 messages instantly, (no questions asked, unlike the usual Facebook protocol).
Facebook Message Cleaner is easy to install and use, and it does exactly what it says it will do. There were no issues with installing or removing it.