It’s an interesting time. Microsoft now maintains three different web browsers:

Internet Explorer 11

Microsoft Edge Legacy (Spartan, v18 and below)

Chromium-based Microsoft Edge (v79+)

If you’re using Internet Explorer 11, you should stop; sometimes, this is easier said than done.

If you’re using Legacy Microsoft Edge, you should upgrade to the new Microsoft Edge which is better in almost every way. When you install the Stable version of the new Microsoft Edge (either by downloading it or eventually by using WindowsUpdate), it will replace your existing Legacy Edge with the new version.

Update: Microsoft has announced that Edge Legacy will fall out of support on March 9th, 2021.

What if I still need to test in Edge Legacy?

If you’re a web developer and need to keep testing your sites and services in the legacy Microsoft Edge, you’ll need to set a registry key to prevent the Edge installer from removing the entry points to the old Edge.

Simply import this registry script before the new Edge is installed. When the AllowSxS key is set to 1, the new Edge installer will keep the old entry point, renaming it to “Microsoft Edge Legacy”:

Thereafter, you can use both versions of Edge on the same PC.

If you didn’t have this registry key set and your legacy Edge entry points have disappeared when you installed the new Edge, you can use the Add or Remove Programs applet in the system control panel to uninstall the new Edge, then set the registry key, then reinstall the new Edge.

Note: If you’re a Web Developer, you should also be testing in the Edge Beta or Edge Dev builds because these will allow you to see the changes coming to Edge before your users do. These builds install side-by-side (replacing no browser) and can be installed from https://MicrosoftEdgeInsider.com.

What if my company has sites that only work in Internet Explorer?

In order to help speed migration to the new Microsoft Edge, it offers an Internet Explorer Mode feature when running on Windows. IE Mode allows IT administrators to configure PCs running Windows 7, 8.1, and 10 such that specified sites will load inside a browser tab that uses the Internet Explorer 11 rendering engine.

IE Mode is not designed for or available to consumers.

Because IE Mode relies upon the IE11 binaries on the current machine, it is not available in Edge for MacOS, iOS, or Android.

IE Mode tabs run inside the legacy security sandbox (weaker than the regular Edge sandbox) and ActiveX controls like Silverlight are available to web pages.

IE Mode does not share a cache, cookies, or web storage with Microsoft Edge, so scenarios that depend upon using these storage mechanisms in a cross-site+cross-engine context will not work correctly. IT administrators should carefully set their policies such that user flows occur within a single engine.

Most Edge browser extensions will not work on IE Mode tabs–extensions which only look at the tab’s URL should work, but extensions which try to view or modify the page content will not function correctly.

In an ideal world, users will migrate to the latest version of Microsoft Edge as quickly as possible, and enjoy a faster, more compatible, more reliable browser. Nevertheless, Microsoft will continue to patch both Legacy Edge and Internet Explorer 11 according to their existing support lifecycle.

-Eric