WebCompat Summit (2015)

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What is the Web Compatibility Summit?

Web Compatibility is an ongoing concern for browser vendors, spec writers, language designers, framework authors, web developers and users alike.

Our goal in organizing a WebCompat Summit is to bring together individuals representing these stakeholders in order to share ideas and problems and to coordinate compatibility, testing and standardization efforts.

If you would like to propose a 30 minute talk, or moderate a panel discussion for one of the sessions please fill out the form at http://goo.gl/forms/UtjFBkLVe7 (on page 2 of form). CFP is closed, however there is still the opportunity to present ideas or topics at the end of the day.

There will also be an "unconference" session at the end of the day where attendees can (more) informally present or hold discussions on topics of interest.

Possible topics include, but are not limited to:

Standards & Web Compatibility

Discussion related to web standardization efforts and how they relate to web compatibility. E.g., specifying legacy features, implementing non-standard features, conformance test suites, etc.

Testing, Tooling & Web Compatibility

Discussion related to automated testing, measuring or crawling the web to understand the impact of removing support for certain web platform features, etc.

Outreach & Web Compatibility

Discussion related to doing "evangelism" or outreach work as it relates to web compatibility.

When and Where


Wednesday, February 18th, 2015.

Start time: 9:30am

End time: 5:00pm


Mozilla Mountain View

Mozilla Headquarters
331 E. Evelyn Ave.
Mountain View, CA 94041
  • Phone Number: +1 650 903 0800
  • Access Details: Please check in at reception on the first floor.
  • Map: https://goo.gl/maps/dy6SE

We have the Commons (110), Polaris (109) and Capella (108) rooms reserved.


You can stream the talks at https://air.mozilla.org/web-compatibility-summit-talks/.


To help us with planning, please fill out the following Google form if you plan on attending or speaking on a topic: http://goo.gl/forms/UtjFBkLVe7.

Summit Schedule

Location: MTV Commons

Time Topic
9:30am Registration and Coffee
10:00am Welcome and Introductions
10:15am - 10:45am "Introduction to webcompat.com", by Mike Taylor (Mozilla) @miketaylr
10:55am - 11:25am "Beyond Vendor Prefixes", by Jacob Rossi (Microsoft) @jacobrossi
11:30am - 1:00pm Lunch in the Mountain View office
1:10pm - 1:40pm "How CSS is being used in the wild", by Alex McPherson @alexmcpherson (QuickLeft)
1:50pm - 2:20pm "Engaging with Web Developers for Site Outreach", by Colleen Williams (Microsoft) @collwilliams
2:30pm - 3:00pm "Web Compatibility Data: A Shared Resource", by Justin Crawford (Mozilla) @hoosteeno
3:00pm - 3:15pm Coffee & Snack Break
3:15pm - 4:45pm Unconference, lighting talks, or whatever else we feel like.
4:45pm - 5:00pm Closing Remarks

Location: Polaris or Capella

9:30 - 5:00pm Hack/work room available

Location: Polaris or Capella

9:30 - 5:00pm Unconference/breakout room available

Web Compatibility Issues

Here is a list of issues related to Web Compatibility. Feel free to add as potential topics of conversation.


  • Sharing contact information without breaching the privacy of the contact.
  • Contact information will not necessary be valid for a long time. What about continuity? Proxy email addresses?

Web Standards and Regression

  • When a Web browser delivers a new feature which is breaking the Web
  • When a Web browser removes a feature which is breaking the Web
  • Measuring the Web for detecting legacy practices or current deployed issues
  • Understanding the locality of issues. Some issues are more acute in some regional markets.

User agent sniffing

  • Legacy detection scripts on the client side
  • Multiple JS all doing a kind of detection
  • Databases with old information about user agents.

How do you solve a problem like UA strings?

Browsers are increasingly using "untruthful" UA strings. For example...

Browsers that falsely use "Mozilla" and "Gecko": Chrome, IE (11+), Opera, Safari, Vivaldi

Browsers that falsely use "AppleWebKit" and "Safari": Chrome, Opera, Spartan, Vivaldi

Browser vendors do this because of widespread browser-sniffing - having a "truthful" UA string would break some websites. Various teams and projects have tried hard to stop browser sniffing but it's clearly not going to go away.

Discussion point 1

What scale of problem is this?

  • Not at all - they're UA strings, just ignore them.
  • Not technically a problem but it's getting out of hand (and they're ugly).
  • This is wrong - it's breaking the web and must stop.

Discussion point 2

Should we do something about it?

  • Is there anything we can safely remove from UA strings, e.g. "Safari" or "KHTML" from Chromium-based browsers?
  • Do we need such precise version numbers?
  • Should browser vendors unite to simultaneously "reset" their UA strings to something that more reflects reality?


  • Chrome 41:

Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36

  • Firefox 35:

Mozilla/5.0 (Windows NT 6.3; rv:36.0) Gecko/20100101 Firefox/36.0

  • IE 10:

Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)

  • IE 11:

Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko

  • Opera 26:

Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36 OPR/26.0.1656.60

  • Safari 5:

Mozilla/5.0 (Windows NT 6.2) AppleWebKit/534.57.2 (KHTML, like Gecko) Version/5.1.7 Safari/534.57.2

  • Spartan:

Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36 Edge/12.0

  • Vivaldi 1:

Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.89 Vivaldi/ Safari/537.36