What tool should a web developer use to interact with code in the browser without restrictions?

A browser extension provides a powerful way for web developers to interact with code directly in the browser without the typical restrictions imposed by the web page itself. These extensions can access and manipulate the Document Object Model (DOM), allow script execution, and communicate with external services, giving developers a unique environment for testing and debugging their code.

The functionality of browser extensions enables developers to observe network requests, analyze web performance, and modify web page elements in real-time, which is essential for developing dynamic web applications. This capability sets browser extensions apart from the other options, which don't offer the same level of direct interaction with the web environment in a flexible way.

While MongoDB is a database solution, REST is an architectural style for networked applications, and HTML5 is a markup language for structuring web content, none provide the specific interactive features that browser extensions do for web developer tasks directly within the browser context.