How do you stay focused when you have to check online resources?

I often struggle with staying focused on the task at hand when I have to read anything online. It can be as simple as checking some docs or StackOverflow. However, before I know it 10-15 minutes have passed due to the inevitable link clicking when reading. How do you avoid getting lost in documentation and losing track of your current task?

I try to keep a daily log on paper and a timer to stay focused and it is often interesting to see what I'm doing by the time the timer rings and try to backtrack how I got there.