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.

solution:

the auto-correct option of the auto-correct tool enables you to add and delete words that do not follow abbreviation rules because:

it is a feature that allows outlook to correct common spelling and typing errors and to replace characters with symbols. we can also can use auto-correct as a shortcut, which means we can type a small string of characters and have those characters replaced by a longer string.