The dual engine advantage of Internet Explorer Mode

Published Jul 13 2021 09:00 AM 15.1K Views


Note: The Internet Explorer 11 desktop application has retired and is out of support as of June 15, 2022, for certain versions of Windows 10. Read the retirement blog >

Whether you're new to IE mode or are already planning for it, here's a closer look at what's going on under the hood and a sneak peek at enhancements to come.

A month ago, we announced that the future of Internet Explorer (IE) on Windows 10 is in Microsoft Edge and that the Internet Explorer 11 (“IE11”) desktop application will retire and go out of support on June 15, 2022, for certain versions of Windows 10. At the core of this announcement is Microsoft Edge and its dual engine advantage that brings the web together—both modern and legacy—into a single browser experience. Side by side in Microsoft Edge are the Chromium engine to open modern websites and Internet Explorer mode (“IE mode”) to open legacy, IE-based websites.


What is Internet Explorer mode?

The best way to understand Internet Explorer mode is to start with its origin story, if you will: it was born of the need to keep critical websites built on older technology running (we call these “legacy sites and apps”), and to run them in the context of today's modern web technology. In the world before Microsoft Edge with Internet Explorer mode, those technologies were clunkily siloed in different browsers; you might have used one browser for one set of tasks, and then needed to switch to the other browser for another set of tasks. Microsoft Edge is your “single browser solution” that brings everything seamlessly together through its dual engine advantage. It's a bit like a hybrid car—you use electric most of the time but can also use gas when you need it.

But this unified experience only works if you feel confident in each engine's compatibility. With IE mode in Microsoft Edge, you can. IE mode's legacy site compatibility works by using the actual MSHTML engine (also referred to as the “Trident” engine) from IE11 to open those legacy websites and applications. While the IE11 desktop application (the interface you interact with to browse the web) will retire next year, the MSHTML engine will not—it will remain a part of Windows and be used to power IE mode. In fact, support for IE mode follows the lifecycle of current and future Windows client, Windows Server, and Windows IoT releases (including Windows 11) at least through 2029, so you can feel confident moving to IE mode as you develop a plan to modernize your legacy websites and applications over the coming years.

By using the MSHTML engine, much of the same site and page rendering functionality found in IE11 is brought forward to IE mode. Document and enterprise modes, Active X controls, and Browser Helper Objects are maintained through the move. Some functionality though is not supported in IE mode such as group policies and settings in IE11 that affect window frames, toolbars, and scrollbars—this is simply because IE mode uses those elements from Microsoft Edge. Here's a handy list of what's supported in IE mode:



All document modes


All enterprise modes


Active X controls (such as Java or Silverlight*)

*Microsoft Silverlight will reach end of support on October 12, 2021. For more details, see Silverlight End of Support.


Browser Helper Objects


IE settings and Group Policies that affect the security zone settings and Protected mode


F12 developer tools for IE (when launched with IEChooser)


Microsoft Edge extensions (extensions that interact with the IE page content directly are not supported)


IE toolbars


IE settings and Group Policies that affect the navigation menu (e.g. search engines, home pages)


IE11 or Microsoft Edge F12 developer tools


So how does Microsoft Edge know when to open a site in IE mode versus using the modern, Chromium engine? For organizations, only sites on your Enterprise Mode Site List will open in IE mode. This gives you the flexibility and control to create the best online experience for your users—you can limit use of IE mode to specific sites that need it and for all other sites, they use the faster, more secure, and more modern browsing experience of Microsoft Edge. Like gas in the hybrid car analogy, IE mode is there for just those times when you or your users need to access legacy websites, and the site list is your way to manage that.

Tip: Use your existing Enterprise Mode Site List if you have one. If you used an Enterprise Mode Site List with Microsoft Edge Legacy or with other modern browsers to redirect legacy sites to open in IE11, you can use that same site list to set up IE mode. It’s a great (and quick) way to get started with IE mode.

If you're wondering how your users will know they are in IE mode, the short answer is, they really won't (and that's by design). The dual engine advantage is a seamless experience for your users—they can fluidly move between modern and legacy sites even within the same tab. The only hint they'll see when in IE mode is a small IE icon in the address bar.


You don't have to take just our word for it though. Since its release, we've seen customers move from IE11 to Microsoft Edge with IE mode with great success. GlaxoSmithKline, a multi-national pharmaceutical organization with 130,000 employees, recently made the switch. John Saenz, head of Modern Workspace at GSK said, “The organization-wide benefit is that with a single browser standard, you know that the experience is the same no matter what department you're in. And you know that if you must provide access to a legacy site, it's going to work.”

Refinements coming to IE mode

Like the Microsoft Edge browser, IE mode will be continually refined to provide the optimal experience for you and your users. Thanks to the incredible partnerships with you and other customers, we've heard your feedback and your desire for updates to the user experience, greater consistency between IE mode and IE11, and new cloud management tools. The first planned batch of enhancements, which land in Microsoft Edge 92 in late July, include:

  • Easier access to IE mode: With Microsoft Edge 92, we've made it easier for your users to access sites in IE mode, even when the site is not part of an IT-controlled site list. This capability prompts users to add a legacy site or app they encounter to a local site list. For SMBs or sole proprietorships with unmanaged devices, this will remove roadblocks for your users and give them the power to access legacy websites even if you don't have (or can't set up) a site list. The next time a user navigates to (in other words, reloads) the legacy website or app, it will open in IE mode.

    Tip: Reload websites in IE mode to help with your compatibility testing. Enabling this feature can help accelerate legacy website compatibility testing for your organization. Instead of waiting to add the legacy website to your site list as a first step, you can easily reload the page in IE mode and begin testing.

  • .mht files automatically open in IE mode: Previously, opening Outlook emails in IE11 would preserve their formatting. With the IE11 desktop application retiring, that functionality will be added to IE mode. Mht files will now automatically open in IE mode in Microsoft Edge, preserving their formatting and style, just like in IE11.

And looking ahead to the fall:

  • [Preview] Cloud Site List Manager: We're excited to soon preview the newest method to manage your IE mode site list: the Cloud Site List Manager. With the Cloud Site List Manager, you can move your IE mode site list from local storage to the cloud, giving you the flexibility to easily access and manage updates to your IE mode site list from the Microsoft 365 Admin Center. You can also create different lists and assign them to different devices groups for even more flexibility managing IE mode. And it's simple for your users—all they need to do is be signed in with their AAD accounts and Microsoft Edge will use it to retrieve the correct site list.

Getting started with the move to Microsoft Edge and IE mode

Regardless of where you are in the process, we have resources ready to help you move from Internet Explorer 11 to Microsoft Edge.

  • If you haven't deployed Microsoft Edge to your organization, we recommend reading the Getting Started guide at the top of the Internet Explorer mode website for an overview of the announcement and end-to-end guidance on how to deploy Microsoft Edge, configure IE mode and evaluate compatibility, and help move your users.
  • If you have already deployed Microsoft Edge and are ready to set up IE mode, we recommend using the Discover and configure sites for IE mode guide in the Microsoft 365 Admin Center. This powerful online guide provides step-by-step guidance to set up your site list for IE mode and evaluate compatibility. With only a few pieces of information from you, this guide automates the process by creating a customized script for use with either Configuration Manager or Group Policy. For more information about this tool, and how to access it if you do not have the correct permissions, see Proven tools to accelerate your move to Microsoft Edge.

Tip: If your website or application has a compatibility issue after you test it in IE mode, reach out to our compatibility team, App Assure, for help. If your website or application works in Internet Explorer 11, it should work in Microsoft Edge. Historically, App Assure has seen app compatibility rates of 99.7%, so if you experience a website or application issue after you’ve set up and tested it in IE mode, reach out to the App Assure team for no-cost help remediating the issue. You can submit a request for assistance through their website or reach out to them directly via email at

Lastly, we've launched a webinar series to answer questions and help you move from Internet Explorer to Microsoft Edge. Follow @MSEdgeDev on Twitter for information on upcoming webinar dates and how to sign up.

As these new IE mode enhancements become available in Microsoft Edge 92 and beyond, know that we are aiming for a truly seamless browser experience for your users' daily workflow and for simplicity in your browser management. Your feedback on these tools, the user experience, and any part of your journey from IE11 to IE mode is highly valued, so please feel free to submit feedback to us, in the Microsoft Edge app, by leaving a comment here, or through other support channels available to you.

Editor's note: This post is part of the IE to Edge blog series, an ongoing series of articles designed to help you move from Internet Explorer 11 to Microsoft Edge! Each will focus on a different relevant topic to help you in your journey, from what to expect when setting up IE mode to what to expect for end users after the IE11 desktop application retires. Look out for more of these blogs as we journey towards June 15, 2022!


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‎Jun 15 2022 06:09 AM
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