The WCAG Contrast Checker is a Firefox extension designed for web developers to ensure compliance with accessibility standards. This tool evaluates the color contrast of all elements on a webpage, taking into account their computed styles, including color and background-color CSS properties. It also accommodates RGBA values by factoring in opacity, providing a realistic assessment of color visibility.

Additionally, the extension features manual input fields for users to test specific color combinations. It automatically refreshes to reflect changes in the DOM, such as the addition or removal of elements, although this feature can be deactivated during extensive modifications. This ensures that developers can maintain an accessible user experience without compromising on design.