Firefox 66 for developers

Draft
This page is not complete.

This article provides information about the changes in Firefox 66 that will affect developers. Firefox 66 is the current Beta version of Firefox, and will ship on March 19, 2019.

Changes for web developers

Developer tools

No changes.

Removals

HTML

  • UTF-8-encoded HTML (and plain text) files loaded from file: URLs are now supported without <meta charset=utf-8> or the UTF-8 BOM making it easier to work on such files locally before uploading them to a server. You still need to make sure that the server sends charset=utf-8 in the Content-Type HTTP header for such files. (The detection mechanism used for local files would break incremental loading in the network case.) (bug 1071816).
  • The x-moz-errormessage attribute has been removed from the <input> element (bug 1513890). You should use Constraint validation features instead.

Removals

CSS

Removals

SVG

No changes.

Removals

JavaScript

No changes.

Removals

APIs

No changes.

New APIs

DOM

DOM events

  • The InputEvent.inputType property has been implemented (bug 1447239).
  • (TENTATIVE, MIGHT NOT HIT 66) The Window.event and Event.returnValue properties — originally proprietary IE features, then also supported across other browsers for compatibility purposes — have been re-introduced in Firefox 65, after first being added in versions 63 and 64 respectively but then removed again due to compatibility issues. 
  • (TENTATIVE, MIGHT NOT HIT 66) From 66 onwards, when the KeyboardEvent.keyCode property of the keypress event object is 0, the value will be the same as KeyboardEvent.charCode. Conversely, when charCode is 0, it will be the same as keyCode. This mirroring behavior matches other browsers and is expected to solve most associated compatibility issues, however user agent sniffing might cause further issues in some JavaScript libraries. Note that in spec terms, we've switched from the split model to the conflated model (see How to determine keyCode for keypress events in the UI Event spec).

Service workers

Media, Web Audio, and WebRTC

Canvas and WebGL

Removals

Security

No changes.

Removals

Plugins

No changes.

Removals

Other

No changes.

Removals

Changes for add-on developers

API changes

No changes.

Removals

Manifest changes

No changes.

Removals

See also

Older versions

Document Tags and Contributors

Last updated by: chrisdavidmills,