What is a Browser Extension?

A browser extension is indeed a tool that customizes the browser's functionality. These extensions are small software programs that can be added to a web browser to enhance its capabilities and offer users various features. For instance, they can block ads, manage passwords, or integrate with other services to improve productivity or the overall browsing experience.

The flexibility and variety offered by browser extensions allow users to tailor their web browsing environment to their specific needs and preferences, thereby significantly enhancing the functionality of the browser beyond its standard features. This makes them invaluable tools for many users who wish to optimize their use of web applications and interactions.

The other choices do not accurately describe what a browser extension is. Core programming refers to the foundational elements of a web browser that enable it to function, rather than the additional features provided by extensions. A server enhances browsing capabilities through backend processing, which is distinct from the frontend modifications that extensions provide. A design layout for websites pertains to the structure or design of web pages themselves, not to the browser's functionality.