OpenTelemetry is the go-to open-source standard for observability, but when it comes to tracking frontend performance and user interactions, things get a little tricky. Unlike backend services, browsers introduce challenges like CORS restrictions, asynchronous execution, and limited access to certain telemetry data. This guide covers everything you need to know about using OpenTelemetry in the browser, from setup to best practices, advanced configurations, and real-world debugging techniques.