The change won't happen overnight: Microsoft talks about changes 'over the next year or so' and there will be a preview version in early 2019 that developers can sign up to test. And while it will simplify compatibility and support for many organisations, there are still plenty of open questions about how these technology changes will happen.
For enterprises, web browsers are both an opportunity and a burden. Securing the browser is a major concern, closely followed by compatibility. Many internal line-of-business applications are browser based, and a substantial number of them still rely on older Internet Explorer (IE) technologies like ActiveX, so compatibility testing has been a stumbling block for Windows upgrades. Microsoft deliberately didn't support those technologies in Edge for security and performance reasons; instead, it provides policy settings where admins can create a compatibility list of URLs that automatically open in IE 11 (including setting which older version of IE the page needs to emulate). That has meant two browsers to manage and update on the desktop: even enterprises that have adopted Chrome or Firefox as their default browser will likely have IE for legacy systems and Mac users have had to use virtual machines to access those systems.
The other half of that problem has been Edge compatibility with public websites, which are frequently tested only for Chrome. The promise of the open web was that web standards would be more robust because they'd be implemented by multiple browsers. In practice, differences in implementation, the way developers frequently implement the vendor-specific versions of new standards (marked by vendor prefixes) and don't update code to the final, un-prefixed standard, along with the popularity of Chrome, have meant that many sites are built for and tested on Chrome even when they use what are technically open web standards. Having Edge limited to Windows 10, so developers on Mac or older versions of Windows have to use virtual machines or testing services to check their code, exacerbates the problem.
Microsoft estimates that the latest Edge is 99 percent compatible with websites that expect Chrome; getting that last 1 percent without web developers testing their sites and submitting bugs seems to have proved uneconomic; without those bugs, the Edge team was reduced to reverse-engineering how sites were coded to support them. And of course, with Edge tied to the six-monthly updates of Windows, even the 50 percent of businesses that have already adopted Windows 10 aren't all on the latest version of Windows 10 and Edge.
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Ideally, that will open the legacy site using the IE engine, but in a tab inside Edge instead of in a separate IE window, even on Mac. Microsoft is hopeful, but not certain, that the Edge team will be able to make this in-tab IE mode work, so it's not a firm commitment — but it would certainly create a much more seamless experience on legacy sites for users.
Building for the new Edge
Microsoft and Google are already working to make Chromium perform well on the ARM64 version of Windows, and Microsoft's commitment to use Chromium in Edge may make that collaboration more successful. Mozilla and Qualcomm are also working on a native ARM64 version of Firefox for Windows on Snapdragon, so your browser choices on those devices won't be limited.
Any sites that organizations have written specifically to work in Edge should also work in the Chromium-based version without significant updates; signing up to the Edge Insider program will give companies early access to test sites.
UWP apps that use EdgeHTML and Chakra will still be supported, and those engines will still be maintained and get bug fixes, Microsoft told us, so there's no immediate need for developers to rewrite them; ChakraCore continues to be developed as an open source project. In future, the web view control might move to using Chromium instead.
The plan for Progressive Web Applications (PWAs) on Windows 10 isn't finalised, but it's likely that they will switch automatically to use the new browser and the Chromium engine, which again shouldn't mean any significant changes are required. (Using PWAs on older versions of Windows previously meant using Firefox or Chrome, as IE didn't have technologies like service workers that PWAs rely on.)
The user experience in Edge will change in some ways with the switch to Chromium, as will the user interface, so organisations will need to notify and possibly train users. The question is how much. For example, Microsoft hasn't said anything about how extension support will work. The Edge extension model is very much the Chrome extension model, just with a much higher bar to get accepted into the Windows Store; we don't know if that will change to give users access to more extensions or whether caution will prevail in order to provide a higher level of security and assurance.
Microsoft intends to contribute code to Chromium to keep the smooth scrolling and ink support it has built into Edge in the new browser, as well as the hardware acceleration that gives Edge better battery life than Chrome. Any improvements to the amount of resources required by Chromium would particularly benefit Electron apps: Microsoft has created one of the most popular and performant apps built on Electron, Visual Studio Code, so that experience may translate to improving Electron generally through improvements to Chromium.
But because Chromium is a community project, it's up to the Chromium community to accept that code into the project. That makes it harder for Microsoft to make commitments on maintaining battery life and other browser features in the new version of Edge, because it will be the Chromium community rather than just Microsoft making decisions about what belongs in the browser engine and how it works.
If the community doesn't want to pick up something Microsoft contributes to the browser engine, Microsoft could choose to implement it and maintain it in Edge outside the browser engine itself, but that's expensive and negates many of the advantages of switching to Chromium in the first place. It may turn out that there will be some features from Edge that just aren't useful enough to justify the cost of Microsoft continuing to support them.
There are other technologies, like the token binding standard that Google recently decided to remove from Chrome just as it got approved by the IETF (despite having co-authored the standard with Microsoft), that seem too strategic for Microsoft to give up on. Token binding is how Microsoft secures long-lived connections to Azure AD and Office 365 from Windows 10. It's more likely that Microsoft will work with the web standards community to create a new specification for token binding that does get accepted (and carry on using its own implementation in Windows 10 in the meantime).
The new version of Edge will take some time to develop, so a new version of token binding may be ready in time. But it remains to be seen how well Microsoft can maintain its own browser priorities once it no longer controls the destiny of its own browser engine.
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Mary Branscombe is a freelance tech journalist. Mary has been a technology writer for nearly two decades, covering everything from early versions of Windows and Office to the first smartphones, the arrival of the web and most things inbetween.