This is a really good question because it gets at the hard truth that money is a great motivator for many reasons; fear of not having enough, a way of keeping "score", a way of quantifying our "worth", etc.
Once we have decided we have enough money and are FIRE, what then? Time could be a motivating measuring stick but even though we know rationally that our days are numbered, most of us can't live with the knowledge on a daily basis. Memento mori is hard! And then in FIRE "free" time has also increased so motivating deadline urgency is also decreased.
What to do, what to do? Everyone needs to find their own answer, and it will change over time. For me I work on big themes rather than specific goals, bolstered by healthy routines and habits. Nothing too granular or oppressive. In fact, I'm trying very hard to quantify much less in all areas and just go with a flow in the general direction I've chosen.
All this to say that you might benefit from some enthusiasms or interests that demand your time and attention and make the interweb surfing less compelling, that is, time spent on FB would feel less worthwhile than something else you've decided is a more enjoyable use of your time.
Or you can take a page from time manager Laura Vanderkam and calculate how many more hours you can expect to live based on the Center for Disease Control's Life Expectancy Tables. Memento mori indeed! (from Off the Clock, pages 10-11)
Whew! I better get off this Forum and on to something else I've been wanting to do.
Good luck!