The new Chromium-based Microsoft Edge will impersonate other browsers depending on the site being visited. This may be done for compatibility reasons, like properly rendering pages or how video will be streamed and played back.

With the release of the Chromium-based Microsoft Edge, Microsoft now uses the Chromium Blink engine instead of it's original EdgeHTML engine. Microsoft has also started to add features that were unique to the original Edge into their new Chromium-based version.

In order to support sites that utilized features that were dependent on Google Chrome or the original Microsoft Edge, the new Chromium Edge browser will switch its user agent to pretend to be a different browser.

Switching User Agents

A user agent is a string that is sent to a web site when a browser connects to it so that site can identify the browser. This allows the site to dynamically make changes in how the site is displayed or what features are offered depending on the browser being used.

When the new Microsoft Edge starts, it will connect to config.edge.skype.com and download a JSON configuration for the browser. Below is the URL that the Microsoft Edge Canary version uses when it starts up.

https://config.edge.skype.com/config/v1/Edge/75.0.131.0?osname=win&channel=dev&clientId=[id]&osver=10.0.18875&osarch=x86_64&osring=WIF&osedition=professional&ostelemetrylevel=full

Microsoft's server will then respond with a JSON config file. This configuration file contains various configuration settings that the browser will use while it is open.

One section of the JSON configuration file is called EdgeDomainActions and is a series of rules that specify what browser Microsoft Edge should impersonate when visiting a particular site. You can see the EdgeDomainActions config section below.

{ "EdgeDomainActions":{ "user_agent_override":{ "version":1, "policies":[ { "name":"EdgeUA", "type":"partialReplacement", "value":"AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/18.17763" }, { "name":"ChromeUA", "type":"edgeTokenReplacement", "value":"" } ], "applications":[ { "domain":"netflix.com", "applied_policy":"EdgeUA" }, { "domain":"facebook.com", "applied_policy":"ChromeUA" }, { "domain":"messenger.com", "applied_policy":"ChromeUA" }, { "domain":"hbonow.com", "applied_policy":"EdgeUA" }, { "domain":"hbogo.com", "applied_policy":"EdgeUA" }, { "domain":"napster.com", "applied_policy":"EdgeUA" }, { "domain":"sling.com", "applied_policy":"EdgeUA" }, { "domain":"stan.com.au", "applied_policy":"ChromeUA" } ] } }, }

This section tells the Edge browser that for certain sites it should impersonate Google Chrome (ChromeUA) or the original Microsoft Edge (EdgeUA).

For netflix.com, hbonow.com, hbogo.com, napster.com, and sling.com, the new Edge will pretend to be the original Edge and switch its user agent to:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/18.17763

For facebook.com, messenger.com, and stan.com.au it will pretend to be Google Chrome and use the following user agent:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3763.0 Safari/537.36

For all other domains not listed, it will use the default user agent, which is:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3763.0 Safari/537.36 Edg/75.0.131.0

Why pretend to be another browser?

There are some popular sites that look better or offer better usability in a particular browser. As the new Microsoft Edge is in the unique position of having the highly supported Blink engine from Chromium, but enhanced video playbook of the PlayReady DRM from Microsoft, it can pick and choose what capabilities it wants to advertise to the site.

For example, this allows it to tell a site that it's Google Chrome if the site work better in Google Chrome browsers. This feature also may allow it to pretend to be the original Microsoft Edge when connecting to video streaming sites in order to take advantage of Microsoft DRMs such as PlayReady, which are not normally supported in Chromium browsers.

While these are all guesses and it is not known the exact reasons for Microsoft switching the user agents, the new Microsoft Edge has become one of the only browsers that can borrow from two platforms so that it can provide optimal performance.