Flight Recorder allows you to generate a configuration script for Flight Simulator by simply browsing the pages you want tested. You can configure your browser so that Flight Recorder will watch you interact with the website and generate a script that, when run with Flight Simulator will copy your actions exactly (well, nearly).
Flight Recorder works by acting as a Proxy Server. Proxy Servers are a normal part of the infrastructure of the web, normaly implemented to provide services such as 'caching' -- which allows some requests to be satisfied sooner. Flight Recorder is actualy much simpler than these systems; it just likes to watch, trying not to change anything that would've happend anyway.
Flight Recorder is implemented as a 'plugin' to the Muffin filtering proxy server. Muffin has many, many features implemented as other plugins, but for our purposes none of these are needed, just Muffin's general proxy framework is used.