You're struggling with some kind of internal conflict about how to use your time. Sometimes you can power through that sort of thing by just telling yourself you HAVE to get going, or with technical measures like Leechblock. But those approaches are unsustainable, because they don't address the fundamental conflict. How do you feel when you're browsing frivolous material? How do you feel when you consider starting to work? How do you feel just before the urge to take a break arises? Get clear on these questions, and you will be clearer about the way forward.