A website test environment invokes multiple instances of a commercial browser, and captures invocations of browser operations for gathering performance data without interference from other instances or multiple occurrences of the operating system (OS). Commercial browsers often employ constraints that assume only a single instantiation is executing on a particular machine. Configurations allow each instance to present as a separate user, thus avoiding conflicts that may arise from temporary files and network connections, for example. Each browser instance operates as a performance agent and dynamically links with a set of entry points for accessing performance related browser operations. As each agent invokes native (OS specific) machine functions for network access via particular entry points, configurations disclosed herein redirect the entry points to a collection layer of instructions (code) for capturing performance data in addition to invoking the native OS function called for by the browser operation.