Ok, a few years ago you could find the URL to your profile picture to get your facebook ID. But facebook changed that, and people who changed their username (https://www.facebook.com/USERNAME) can't find their ID. So I have this little trick. Its really easy. Enjoy =)
Step 1: Find Your Username (or Set One)
Ok, go to your account settings (https://www.facebook.com/settings?ref=mb ) and look at the username box. If you can now find your username (look in picture) it should be in the middle of the page. If it is not set, press the edit button and set it.
Step 2: Find Your ID
TheSEOTools made it!