Cross-browser testing is crucial for ensuring that web applications and websites work properly across different browsers, devices, and assistive technologies. It involves determining if the website or application can be accessed through various combinations of browsers, operating systems, and devices. With the constant changes in browser functionalities and updates, cross-browser issues can arise, leading to slow page times, errors, and poor user experience. To address this, developers need to adopt a holistic approach to testing, including manual and automated methods, to ensure that their application works as expected on all browsers and devices. By implementing cross-browser testing, developers can gain peace of mind knowing that their web application or website is compatible across multiple browsers, old and new. Tools like New Relic can provide real-time insights into user experience, helping developers identify and address errors quickly.