This article provides information about the changes in Firefox 74 that will affect developers. Firefox 74 was released on March 10, 2020.
Changes for web developers
$x()web console helper's third argument (result type) now accepts simple string values as well as
XPathResultconstants (bug 1602591).
- Freshly landed support for the optional chaining operator "?." which can also be used with Console's autocomplete (bug 1594009).
- The Debugger can now inspect and debug nested workers (bug 1590766)
text-underline-positionis now enabled by default (bug 1606997).
text-decoration-thicknessproperties now accept percentage values (bug 1607534).
autovalue of the
outline-styleproperty has been enabled by default (bug 1031664).
-moz-prefixed-Multiple-column layout properties have been removed (bug 1308636). See the Firefox Site Compatibility Notes for more details.
- The Optional chaining operator has been implemented (bug 1566143).
document.locationproperty, for example) was the originating
Object.toSource()method and the global function
uneval()are no longer available for use by web content or extensions (bug 1565170).
- Firefox 74 now supports the
languagechange_eventevent and its companion event handler property,
onlanguagechange, which is triggered when the user changes their preferred language (bug 1154779). This was previously listed in our compatibility database as supported from Firefox 3.5, but this was in error.
Canvas and WebGL
TextMetricsinterface has been extended to contain four more properties measuring the actual bounding box —
actualBoundingBoxDescent. Text metrics can be retrieved using the
CanvasRenderingContext2D.measureText()method (bug 1102584).
- The non-standard
IDBDatabase.mozCreateFileHandle()method has been removed, in favor of the (also non-standard)
IDBDatabase.createMutableFile()method (bug 1024312).
- The non-standard
IDBMutableFile.getFile()method has been removed (bug 1607791).
- The non-standard
mozGetAsFile()has been removed, after being deprecated several years ago (bug 1588980).
isReloadhas been removed, from both Firefox and the specification (bug 1264175).
- Feature Policy is now enabled by default! Use the
allowattribute (and the
allow) to set permissions for your frames (bug 1617219).
Cross-Origin-Resource-Policyheader is now enabled by default (bug 1602363).
- TLS 1.0 and 1.1 support has been removed from Firefox; you'll need to make sure your web server supports TLS 1.2 or 1.3 going forward. From now on, Firefox will return a Secure Connection Failed error when connecting to servers using the older TLS versions (bug 1606734).
- Starting in Firefox 74, when a site delegates permission to access a resource to embedded content in an
allowattribute, and the embedded page requests permission to use that resource, the parent page prompts the user for permission to use the resource and share it with the embedded domain, rather than both the outer and inner pages prompting the user for permission. If the outer page doesn't have the permission requested by the
<iframe>is immediately denied access without prompting the user bug 1483631.
Changes for add-on developers
- Shortcut keys can now be unassigned in
Commands.updateby passing an empty value of
urlclassifications are now returned as part of the
detailsin each event of
webrequest, providing information on whether a request is classified as fingerprinting or tracking bug 1589494.
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