Put a timer in the corner of nearly any webpage

web_timer.js

// Click to (re)start, shift-click to increment, ctrl-click to decrement
// Customize the initial time (currently 60 seconds), size, and position
// Copy-paste into dev tools (CTRL-SHIFT-i)

(function() {
  var init_time = 60, size = 1.5, position = "top right";
  var t = init_time;
  var e = document.createElement('div');
  e.style.position = "fixed";
  position = position.split(" ");
  e.style[position[0]] = "5px";
  e.style[position[1]] = "5px";
  e.style.zIndex = "2147483646";
  e.style.backgroundColor = "#294";
  e.style.padding = "0.3px 0.5em";
  e.style.borderRadius = "4px";
  e.style.fontSize = size+"em";
  e.style.color = "#fff";
  e.style.minWidth = "2em";
  e.style.textAlign = "center";
  e.style.cursor = "pointer";
  document.body.appendChild(e);
  function redraw() {
    e.innerHTML = (Math.floor(t/60)+":"+(t%60)).replace(/:(\d)$/, ":0$1");
    e.style.backgroundColor = t>=10 ? "#294" : "#932";
  }
  redraw();
  var ii = -1;
  function reset(ev) {
    if (ev.shiftKey) {
      t = Math.ceil(t/15+0.1)*15;
    } else if (ev.ctrlKey) {
      t = Math.floor(t/15-0.1)*15;
    } else {
      t = init_time;
    }
    redraw();
    if (ii>=0) window.clearInterval(ii);
    ii = window.setInterval(function() {
      if (t>0) {
        t--;
      } else {
        window.clearInterval(ii);
      }
      redraw();
    }, 1000);
    return false;
  }
  e.onmousedown = reset;
  e.ontouchstart = reset;
})();