Visually obscures a web page, to encourage testing screen reader navigation.
Web developers must test that all pages and components they create can be interpreted appropriately by assistive technology, such as screen readers (https://www.w3.org/WAI/perspective-videos/speech/).
In principle, they can test screen reader functionality by simply not looking at the page.
In practice, however, a developer who does not experience visual impairments might find it difficult to overcome the instinct to look at what they are doing.
When activated, this extension visually obscures everything in the viewport, so that the developer must use the screen reader to interpret the page content.