Fire Source Viewer is a Firefox WebExtension designed for web developers and IT professionals, facilitating the quick viewing of HTML, JavaScript, and CSS source code. This tool enhances readability through a syntax highlighter and beautifies the code, making it easier for users to analyze and understand the structure of web pages. Users can benefit from features such as line numbers, file size, and cache header display, which provide essential information at a glance.

Additionally, the extension includes a toolbar icon that indicates JavaScript node counts, aiding in the assessment of script complexity. Users can easily copy source code to their clipboard for further use. However, it is important to note that the WebExtension operates only on websites that permit content scripts, which may limit its functionality in certain contexts.