DOM events changes introduced in Firefox 66
Firefox 66 introduced the following DOM events changes for compatibility with legacy content:
- The Window.event and Event.returnValue properties — originally proprietary Internet Explorer features, then also supported across other browsers for compatibility purposes — have been added in Firefox 66.
If you maintain legacy intranet or hosted software that depends on Firefox not supporting these, the following preferences exist to opt into the pre-Firefox 66 behavior:
These preferences take a comma-delimited list of domains as a value. For example, internal.example.com or staging.example.com.
These preferences can be set via the new Preferences enterprise policy.
Support for window.event can be disabled by setting dom.window.event.enabled to false.