How to get the xs value from Facebook cookie with Google Chrome:
- Open www.messenger.com
- Open Developer Tools
- Click "Application" tab
- Click, "Cookies" in the left panel
- Click "www.messenger.com"
- Copy the value of "xs"
Word of warning
This value is to be used in fb-sleep-stats
config file (development.json). But PLEASE do not share this with anyone else, since it provides access to your Facebook account.
Ok, so here's the way to do it on Firefox: