What is cross-browser testing?

Cross-browser testing confirms the application works consistently across browsers and versions - Chrome, Firefox, Safari, Edge - and often across operating systems. Differences appear in CSS layout, JavaScript APIs, date pickers, fonts, and cookie/storage behavior. Teams pick a supported browser matrix based on analytics and customer contracts rather than testing every combination infinitely. Automated UI runners execute the same flows on multiple browsers in CI or grids; manual spot-checks still help for new UI patterns. Responsive testing on mobile viewports is often bundled with cross-browser work. Focus on browsers your users actually use; emulate legacy only if revenue or compliance requires it. One passing run in Chrome does not guarantee Safari parity.