The new Microsoft Edge web browser that will be included in all versions of Windows 10 will not be using many of the old features and technologies that have been a part of the old Internet Explorer browser for many years.
Overall, over 300 APIs that were a part of Internet Explorer won't be included in Microsoft Edge, and the browser team has also removed 220,000 lines of old IE code from Edge as well. One of the more well known APIs that won't transfer from IE to Edge is ActiveX, which allowed developers to create web browser add-ons in IE. Here's why ActiveX won't be needed for Microsoft Edge:
"The need for ActiveX controls has been significantly reduced by HTML5-era capabilities, which also produces interoperable code across browsers. Microsoft Edge will support native PDF rendering and Adobe Flash as built-in features rather than external add-ons."
Another API that didn't make the cut is Browser Helper Objects, which gave developers a way to release third-party toolbars for IE. There will be no BHO support for Edge in favor of Chrome-like extensions, but a replacement will come after Windows 10 is released. Here's why:
"We recently demonstrated our early work on a modern, HTML/JavaScript-based extension model to provide extensibility beyond what is available with HTML5. We will enable this new model after our initial release of Microsoft Edge this summer and we look forward to sharing more details soon."
While Windows 10 for phone and the version made for tablets will use Microsoft Edge exclusively, notebooks and desktop PCs with Windows 10 will still contain a version of IE11, mainly for businesses who still need it to run legacy technologies on their websites.
Source: Microsoft
