Cross-Browser Testing

You can't test every browser × OS × version combination, so cross-browser testing is really about prioritising sensibly and knowing where engines genuinely differ. This sheet is the matrix and the gotchas; for layout-size coverage see Responsive Testing, and for tooling see the device-cloud tools linked below.

The engines (this is what really varies)

Testing one browser per engine catches most rendering differences. iOS is special: every iOS browser uses WebKit, so "Chrome on iPhone" is really Safari's engine.

Prioritising coverage

1. Pull your analytics — test what your users actually use.
2. Cover the three engines at minimum.
3. Add the current + previous version of each major browser.
4. Don't forget Safari on iOS — usually the biggest gap.

Where bugs cluster

• Date/number/<input type> rendering (esp. Safari).
• Flexbox/grid edge cases and gap support.
• New CSS/JS APIs not yet in Safari/older browsers (check support first).
• Font rendering and form-control styling.
• Autoplay, storage, and cookie policies differing per browser.

Common mistakes

• Testing many Blink browsers (Chrome, Edge, Brave) and calling it "cross-browser" — it's one engine.
• Skipping real iOS Safari (emulators ≠ the real thing).
• Coverage chosen by gut, not analytics.
• Ignoring the previous browser version users haven't updated from.

Run automated suites across engines with a device cloud (BrowserStack, LambdaTest, Sauce Labs) — linked below.