Editor locks up when adding an element for HTML5 devices on Mac

The editor will freeze when adding an element inside of the HTML5 Devices section of Project Settings. When the editor is relaunched, the element that was attempted to be added will be present in the Available browsers. This issue previously occurred on Windows in 4.14 but is no longer reproducible.

1. On a Mac machine, create a Blueprint project.
2. Click Edit > Project Settings...
3. Under Platforms, select HTML5 SDK.
4. Select the + icon next to the Available browsers.

Result: Editor will lockup