Microsoft Edge improves HTML5 support on Windows 10 build 14901

While users are still installing the Anniversary Update on their computers, it doesn't mean that development of Windows 10 has concluded. Microsoft is already working on "Redstone 2", and the first test preview for the next version of the operating system is now rolling out to Insiders.

Windows 10 build 14901 is now available for Insiders with PCs enrolled in the Fast ring. According to the company, the new version doesn't introduce any significant changes, as the development team is currently making structural improvements to OneCore (the shared "heart" of Windows across devices) to get the operating system ready for new features. However, if you look closely, you'll see some real improvements coming to Microsoft Edge.

Improvements for Microsoft Edge on build 14901

Starting with Windows 10 build 14901, Microsoft Edge version number jumps from 38.14393 to version 39.14901.

Microsoft Edge version 39 doesn't bring new visual elements or features but compared to version 38 there some exciting new changes inside the Developer Settings, which you also know it as the about:flags page.

Under Composition, you can now select between Selfhost, Stable, and Canary composition engines, which replaces the Windows.UI.Composition option.

In the WebRTC section, we're also seeing that Microsoft is adding a new option to enable WebRTC 1.0 in the web browser. (For those unfamiliar, WebRTC stands for "Web Real-Time Communication", and it's a web standard that allows support voice, video, text, and peer-to-peer file sharing without the need for an extension.)

Then there is the new "Service Workers" feature, which allows Microsoft Edge to support rich offline experiences, push notifications, background sync, cash storage, and other functionalities that usually would require a native application.

The currently available options in the experimental settings are:

  • Enable service workers
  • Enable push notifications
  • Enable background sync
  • Enable service worker cache storage

Finally, this new version of the web browser also includes a new network option called "Fast Networking," which allows you to enable fetch based network stack.

Improved HTML5 support

Although seeing more web standards coming to Microsoft Edge is always good news, perhaps what's more important is how well these new features make Microsoft Edge score on HTML5test.

An HTML5test score helps to define how well a web browser supports HTML5 standards and many other web specifications. Microsoft Edge version 39 scores 500 out of 555 possible points, which is very impressive. However, it's important to note that the high score is only possible when certain experimental features are enabled on Edge.

Out of the box, Microsoft Edge version 39 scores 460 points, which is 32 fewer points than the 492 points Google Chrome scores with the default settings, but turning on specific experimental features boost the browser to an impressive 500 points.

If you're running Windows 10 build 14901, you can test the score by turning on all the experimental features in the about:flags page, but making sure you leave the following options disabled:

  • Allow Adobe Flash Player localhost loopback
  • Allow unrestricted memory consumption for web pages
  • Disable Pointer event interfaces
  • Use legacy set internal behavior

Also, you must configure the four combo boxes with the following options:

  • Composition engine to Canary
  • Enable touch events to Only on when a touchscreen is detected
  • Fire compatible mouse events in response to the tap gesture to Only on when touch is enabled
  • Enable VP9 video format to Automatic

Then restart the browser and go to to see the test results for Microsoft Edge.

It's important to point out that the HTML5test is not a speed test. It's only a test that checks what HTML5 and other web standards a particular web browser supports.

What do you think about the new improvements on Microsoft Edge for Redstone 2? Tell us in the comments below.

More Windows 10 resources

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Mauro Huculak

Mauro Huculak is technical writer for His primary focus is to write comprehensive how-tos to help users get the most out of Windows 10 and its many related technologies. He has an IT background with professional certifications from Microsoft, Cisco, and CompTIA, and he's a recognized member of the Microsoft MVP community.