Five Years After Edge Legacy Ended, a Retrospective Recalls Its Scrolling and EPUB Reader

The author uses 'Edge' to mean Edge Legacy, not the Chromium-based Microsoft Edge that inherited the name. Although Edge Legacy is no longer a standalone browser in the public eye, the article notes that EdgeHTML, MSHTML and the newer WebView2 remain in Windows as components that provide web rendering for UWP apps. No complete retirement timetable has been set.

The browser grew out of Microsoft's effort to move beyond Internet Explorer in the Windows 10 era. IE 11 had added modern features, but IE was visibly struggling, and the long tail of IE compatibility made changes to MSHTML difficult. EdgeHTML was created with a new user-agent string, no IE compatibility mode, support for modern web standards and what the article describes as significantly improved performance. Microsoft also had a chance to redesign the browser UI and features.

On Nov. 11, 2014, Microsoft introduced a 'living Edge document mode' in a Windows 10 preview and announced more than 2,000 interoperability fixes and 20 new platform features. At that point Edge still appeared as a new mode of IE, but it already carried core EdgeHTML ideas: making the web modern without breaking enterprise browsing. The article cites a Microsoft blog post explaining why the company did not adopt WebKit. Microsoft wrote that the web is built on multiple independent yet interoperable implementations of web standards and that it felt it was important to counter movement toward a monoculture on the web. Starting from its own engine, especially one unshackled from legacy compatibility concerns, would deliver an interoperability-focused engine faster, Microsoft said.

The article argues that independent browser engines have value. It cites Mozilla's position that when innovation depends on a single dominant engine, technical and economic power concentrates, choices narrow and the web's direction may serve a few large platforms rather than the public interest. Browser engine diversity, Mozilla said, helps keep technology people-first rather than shareholder-first. The article also warns that a lack of engine diversity can mean some APIs receive less scrutiny or that one company's commercial goals can quickly affect the web broadly. If Chromium were the only engine, the article says, Google could manage or even ban content across the internet. Mozilla published 'Goodbye, EdgeHTML' when Edge Legacy died, according to the article.

Microsoft unveiled Project Spartan in January 2015, explained the new engine in February and named the browser Microsoft Edge on April 29. It shipped with Windows 10 on July 29, 2015. From 2015 to 2018, EdgeHTML's major versions moved with Windows 10 feature updates, from EdgeHTML 12 to EdgeHTML 18. The article lists improved compatibility with other browsers, modern DOM typography and better performance, browser extensions and Edge 18 among important engineering steps.

The article says Edge started well by prioritizing APIs used by other major browsers and real websites, rather than only counting features on standards lists. Microsoft used a large number of URLs crawled by Bing to find commonly used code and fix compatibility problems faster. Changing the user-agent string meant giving up IE mode, exposing more problems to modern websites and fixing them. The long-term goal was for EdgeHTML to run the same code as other browser engines. Edge also leaned on Windows system APIs such as Media Foundation, Windows Imaging Component and DirectWrite for better performance and lower power consumption. Its PDF rendering used the WinRT PDF renderer, and EPUB had what the author calls an excellent rendering engine.

That reliance on Windows also bound Edge tightly to the operating system. It could not easily be ported to other systems or even brought down to Windows 7, a decision the article says foreshadowed EdgeHTML's death. The author singles out scrolling as a generational experience. Edge did not simply convert each wheel input into a fixed distance; it added a velocity curve over time. During continuous scrolling, new input modified the animation already underway, producing inertia that still felt responsive. It also calculated scroll distance according to the size of the scroll container, so the same wheel action could move farther in a larger page area. Edge worked closely with DirectComposition and Direct Manipulation. Its scrolling was asynchronous, so it did not stutter when the page was busy, and the article says Edge was the only browser that supported asynchronous sidebar scrolling. That experience, too, was not easily ported.

The author calls Edge the best EPUB reader. EPUB was removed from the last Edge version, and the article says users who want it must uninstall update KB4601383. Even so, the author writes, Edge offered smooth scrolling, a full browser and strong UX design, in contrast with what the article describes as Calibre's janky reading experience. EPUB rendering was reflowable and paginated, and not based on shadowroot, which gave elegant and high-performance page turning, better than readers limited to scrolling. All pages supported ink annotation and circling.

Font rendering was another difference. Chromium used Skia at the time, while Edge used Windows' DirectWrite. The article says Skia's hardcoded settings made text slightly thinner than the Windows default, with the difference more visible in CJK characters. After Chrome 132, Chromium accepted a patch from the Edge team that brought font rendering closer to the original Edge experience.

Edge's distribution limited its reach. It was offered only on Windows 10 for PC users, and major platform features arrived with Windows' twice-yearly feature updates, which many users did not install. Enterprises that delayed system upgrades could not get new EdgeHTML features through independent browser updates the way Chrome or Firefox users could, creating incompatibilities between Edge versions. A 2019 Verge interview cited in the article noted that enterprise testing and delayed deployment of Windows feature updates kept Edge behind. Extensions were not available on day one, leaving the extension community immature. Edge's user base remained low, feeding a cycle in which developers did not test for Edge. The article notes that Windows allowed third-party browsers, unlike iOS.