Tuckit

Tuckit is a Pomodoro and focus timer that lives on the edge of every page. Drag the rope inward, let go, and the timer starts - 5 minutes to 4 hours, or a whole Pomodoro run in one gesture. It keeps running as you move between tabs, blocks the sites you name while you focus, and records what you actually did - including the gap between the time you asked for and the time you really spent. Free, no account, and nothing leaves your machine.