Whether it's checking Facebook or following the news, constant access to the Internet can be a very distracting temptation. We all deal with avoidance on a daily basis and when you're finding writing that essay particularly troublesome; that distraction can become avoidance all too easy. There is a good reason student flats become strangely tidy around revision time. In the same way your web browser makes it very easy to avoid doing work that simply needs to be done: how often have you been working away only to have a little voice in your head asking "I wonder if anybody's tweeted me in the last 5 min?"
There are lots of tools that can help this kind of thing such as using a stopwatch and doing 15 min bursts of work. A good solution for the web browser temptation is to block yourself from being able to see those particularly tempting websites. ‘Nanny for Chrome’ is a simple extension for Google's Chrome browser that allows you to limit what websites you can access, when you can access them, for how long in a day you can access them and many other options that help you avoid the distraction. Importantly, it also makes it very difficult to get round your rules once you've set. There are many other tools like this available that can help you control your distracting influences to have a think about what keeps you from working the way you want to; sometimes the solution can be as simple as a Post-it note.
So if you use Chrome, go to the chrome Web store and have a look.
Note: Firefox users can use an extension called Leech Block to get the same results.