A browser ___ is a separate program that adds a variety of useful features to the web browser, such as sending instant messages or playing mobile-style games.

The correct option is;

Extension

Explanation:

A browser extensions are available small applications plug-ins that allow the modification of the web browser by customizing and changing how information flows through the browser. Browser capabilities include the hosting of varying forms of browser extensions, and settings for ad blocking. Web experiences are vastly enhanced by browser extensions by providing personalized experience.

there is no universally accepted definition of art. although commonly used to describe something of beauty, or a skill which produces an aesthetic result, there is no clear line in principle between (say) a unique piece of handmade sculpture, and a mass-produced but visually attractive item. we might say that art requires thought - some kind of creative impulse - but this raises more questions: for example, how much thought is required? if someone flings paint at a canvas, hoping by this action to create a work of art, does the result automatically constitute art?