Browsers used by Office Add-ins

Office add-ins are web applications that are displayed using iFrames when running in Office on the web and using embedded browser controls in Office for desktop and mobile clients. Add-ins also need a JavaScript engine to run the JavaScript. Both the embedded browser and the engine are supplied by a browser installed on the user’s computer.

Which browser is used depends on:

  • The computer’s operating system.
  • Whether the add-in is running in Office on the web, Office 365, or non-subscription Office 2013 or later.

The following table shows which browser is used for the various platforms and operating systems.

OS / Platform Browser
Office on the web The browser in which Office is opened.
Mac Safari
iOS Safari
Android Chrome
Windows / non-subscription Office 2013 or later Internet Explorer 11
Windows 10 ver. < 1903 / Office 365 Internet Explorer 11
Windows 10 ver. >= 1903 / Office 365 ver < 16.0.11629 Internet Explorer 11
Windows 10 ver. >= 1903 / Office 365 ver >= 16.0.11629 Microsoft Edge*

* When Microsoft Edge is being used, the Windows 10 Narrator (sometimes called a "screen reader") reads the <title> tag in the page that opens in the task pane. When Internet Explorer 11 is being used, the Narrator reads the title bar of the task pane, which comes from the <DisplayName> value in the add-in's manifest.


Internet Explorer 11 does not support JavaScript versions later than ES5. If any of your add-in's users have platforms that use Internet Explorer 11, then to use the syntax and features of ECMAScript 2015 or later, you will need to either transpile your JavaScript to ES5 or use a polyfill. Also, Internet Explorer 11 does not support some HTML5 features such as media, recording, and location.

Troubleshooting Microsoft Edge Issues

Chromium-based Edge is installed on my development computer, but my add-in does not use it

The base browser in Microsoft Edge has changed to Chromium. The older base, called EdgeHTML, is not removed when Chromium-based Edge is installed. Office will still use the EdgeHTML base for add-ins until a build of Office 365 that supports Chromium is installed on the computer. We expect these builds to ship in 2020. They will likely appear in the Insiders channel in the first half of the year.

Scroll bar does not appear in task pane

By default, scroll bars in Microsoft Edge are hidden until hovered over. To ensure that the scroll bar is always visible, the CSS styling that applies to the <body> element of the pages in the task pane should include the -ms-overflow-style property and it should be set to scrollbar.

When debugging with the Microsoft Edge DevTools, the add-in crashes or reloads

Setting breakpoints in the Microsoft Edge DevTools can cause Office to think that the add-in is hung. It will automatically reload the add-in when this happens. To prevent this, add the following Registry key and value to the development computer: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\16.0\Wef]"AlertInterval"=dword:00000000.

When the add-in tries to open, get "ADD-IN ERROR We can't open this add-in from the localhost" error

One known cause is that Microsoft Edge requires that localhost be given a loopback exemption on the development computer. Follow the instructions at Cannot open add-in from localhost.

See also