Firefox Add-on - Simple Timer + Clocks

Simple Timer + Clocks is a Firefox add-on that offers count down timers, stop watch settings, and a clock reminder. Simple Timer + Clocks can be used to run multiple timers simultaneously to track the time you spend on different tasks. Once installed, Simple Timer + Clocks appears as a small alarm clock icon in the status bar of your browser. 

Applications for Education

If you occasionally find yourself struggling with the pacing of your class or with providing sufficient "wait time", Simple Timer + Clocks could be a handy tool to have open on your laptop. Simple Timer + Clocks could also be used track the time students spend completing tasks online.

If you don't want to install anything on your computer, a good web-based timer is Online Stopwatch.