This presentation was given at the 2009 AJAX Experience Conference by Gomez's CTO Imad Mouline and Director, Agent Technology. Today’s browser diversity brings new challenges to Web designers and developers. JavaScript loads and performs differently across browsers such as Internet Explorer 7 and 8, Firefox, Safari and Chrome, and can lead to inconsistent content rendering, poor Web performance, and frustrated end-users. Traditional methods for Web performance testing and monitoring cannot find and diagnose browser-specific, client-side performance problems. This session was designed to help developers learn how to: • Improve content rendering across multiple browsers and operating systems • Understand and improve object load order, browser by browser • Ensure that third-party content doesn’t degrade client-side performance • Realistically preview performance under load in each browser.

1. Web Compatibility and
Performance Testing in
a Multi-Browser World
Imad Mouline, CTO, Gomez
(@imadmouline)
Buddy Brewer, Director of Engineering, Agent Technology, Gomez
(@bbrewer)

2. Agenda
• The problem and the upside
• Functional validation across browsers
• Performance optimization across browsers
• Raw vs. perceived performance
• Key takeaways and Q&A

3. The Problem
• Building applications is more complex
• Developers now support an interrelated mess
of technologies that differ from browser to
browser
• Networking stack
• JS engine
• Rendering technologies (CSS, Canvas, SVG)

4. The Upside
• Browsers provide better performance, richer
functionality
• The rate of change is accelerating, with
competition between vendors leading to
massive gains in performance

5. How?
• We need to understand how our applications
perform in real browsers on the real network
• We need to know both what users encounter
and what they perceive

6. Asymmetric Advantages of Modern
Browsers
• Dramatically faster JS engines
• Greater connection parallelism
• Client side storage
• Native CSS selectors
• 2D compositing (Canvas, SVG)

7. Testing Presentation
• Bespin determines browser Canvas support
at runtime
• Which browsers provide adequate support?

8. Yes: Firefox 3.5, Safari 4

9. No: Firefox 2, Safari 3, Any IE

10. Maybe: Chrome

11. Functional Validation
• As new versions ship, do the expected
browsers still work?
• As new browsers are released, do our
applications still work?

12. Revisiting Performance Optimization
• Are our old techniques still relevant as the
browsers we target evolve?
• Example: Domain sharding
• Legacy browsers allow 2 connections per hostname
• Domain sharding increases parallelism to boost
static object performance via pointing multiple
hostnames to the same host

13. Optimizing IE6 Behavior
• For older browsers, this could represent an
easy 50% load time savings

14. Optimizing IE6 Behavior
• What’s the catch?

15. De-optimizing IE8 Behavior
• In IE8 (and Firefox and Safari and Chrome) using
domain sharding leads to a glut of simultaneous
connection creation and a dramatic performance hit

16. Lessons
• Optimization techniques must evolve along
with the browsers
• So, performance testing should take into
account browser differences
• And to do that, we need to know what
browsers are visiting our site

17. ▪ Difference between quickest and slowest browser load time
equals 13.226 seconds
▪ Large sample of US end-users, on broadband connections, visiting a particular page on a web site over
a 48 hour period
Performance Differences by Browser

18. ▪ Load time for MS Internet Explorer higher than Firefox
▪ Perceived render time for MS Internet Explorer lower than Firefox
▪ Perceived render time is the amount of time needed for the page layout to stabilize and for all content
visible to the end-user above the fold to be completely rendered
Load Time vs. Perceived Render Time

19. Optimizing Perceived Render Time & User
Experience
• Most prominent
image on site loads
almost last
• Changing load order
will not impact raw
page performance,
but will improve
perceived render
time and user
experience

20. What is the download order?

21. Factors that impact object download
order
• Browser type / version
• Host latency, concurrency differences
• Geography
• Geography???

22. San Jose

23. Boston

24. Page Load TimeCache Level
Browser Cache Impact

25. Takeaways – Summary
• Know your end-users
• Identify where and how they use your application,
how they connect to the network, when they do it,
where they do it from, what browser they use, etc…
• Deliver on their expectations
• Know your entire application
• Build performance into your process
• Improve raw, workflow, and perceived performance
• Continuously evaluate your performance targets
• Measure what matters
• Measure from your end-users’ perspective
• Align your end-users’ web experience with your
requirements and ultimate business goals

26. Please complete
an evaluation.

27. Questions?