Timer, Alarm & Stopwatch Pro by Thể Thao BK8

Timer, Alarm & Stopwatch is an extension that lets you easily set a timer, alarm, or adjust stopwatch in your browser.

The interface for this addon can be opened in toolbar popup, a new tab, or a stand-alone window. Simply right-click on the toolbar button to choose the desired context. When you open the UI, there are three tabs on the left side, please click on each tab to see the details. At the top, there is a button to add a new timer or alarm. Click on this button to adjust the timer or alarm settings. For the stopwatch tab, there are the start, reset, and lap buttons.