Browser extensions have a significant impact on both system performance and security. While some extensions provide useful features, others may be poorly coded or maliciously designed, posing a threat to your computer's stability. Extensions consume system resources which can slow down browsing speed and overall performance. Moreover, certain extensions might compromise user privacy by collecting data without consent or injecting ads into web pages. It is essential to carefully review installed browser extensions regularly to ensure they are safe and necessary for optimal system health.