Does Edge's IE Mode Run Silverlight?

When Microsoft retired Internet Explorer 11, it pointed organizations with legacy web apps toward Internet Explorer mode in Edge — a compatibility feature that renders designated sites with the IE engine inside the Edge browser. The official IE11 retirement announcement presents IE mode as the sanctioned path for sites that still depend on IE-era technology.

So the natural question for anyone holding a Silverlight app: does IE mode load the Silverlight plugin?

The short answer

IE mode is built for IE-era web technologies such as ActiveX-based line-of-business sites, and because it uses the Internet Explorer engine, environments that still have the Silverlight plugin installed have sometimes been able to load Silverlight content through it. But treating that as a plan is a mistake, for reasons that have nothing to do with whether a page happens to render today.

Why IE mode is not a Silverlight strategy

Silverlight itself is out of support. Microsoft's Silverlight end-of-support announcement is unambiguous: support ended on October 12, 2021. No security fixes, no compatibility fixes, no assistance. Whatever container you run it in, the plugin is frozen, unpatched software.
You are stacking one legacy layer on another. IE mode exists to buy time for legacy sites, not to host them forever. Building your continuity plan on a compatibility mode wrapping a retired engine loading a retired plugin means three separate deprecation clocks are ticking against you.
Unpatched software is a managed risk, not a free one. U.S. government guidance on enterprise patch management, NIST SP 800-40 Rev. 4, treats software that can no longer receive patches as something an organization must explicitly plan around — typically by isolating it and scheduling its replacement, not by quietly extending its life.
It only helps managed Windows environments. IE mode is a Windows/Edge feature that administrators configure per site. It does nothing for customers, partners, or anyone on a Mac, a phone, or an unmanaged machine.

What IE mode is actually good for

Used honestly, IE mode is a bridge: it can keep an internal legacy app reachable for a defined period while a replacement is built. If that is your situation, the constructive move is to spend the bridge time well — inventory the Silverlight app so you know what a rewrite actually involves, and understand the risks of keeping it deployed so the bridge has an agreed end date.

The question to ask instead

Rather than "can we still open it somewhere?", the productive question is "what should this app become?" For most former Silverlight web apps the candidates are Blazor for staying in the browser with C# — see our comparison with Silverlight — or a desktop rebuild where that fits the users, covered in when WPF makes sense. IE mode can keep the lights on while you decide; it cannot be the decision.

Does Edge's IE Mode Run Silverlight?