DrawR

This extension allows you to draw on the current web page, pick the line colour and thickness and take a screenshot. You can also choose to draw circles, rectangles and straight lines. The screenshot is automatically downloaded in the browser.

Click to draw freehand.
Hold Shift whilst clicking to draw a straight line.
Hold Ctrl whilst clicking to draw a circle.
Hold Alt whilst clicking to draw a rectangle.

Ctrl + Shift + S - triggers the popup and starts the extension on the page.
Ctrl + Shift + Q - triggers clearing the drawings and closing the extension (with a prompt to confirm).