Firefox 68 for developers

This article provides information about the changes in Firefox 68 that will affect developers. Firefox 68 was released on July 9, 2019.

Changes for web developers

Developer tools

Browser/web console

  • The Web console now shows more information about CSS warnings, including a node list of the DOM elements that used the rule (error 1093953).
  • You can now filter content in the Web console using regular expressions (error 1441079).
  • The Browser console now allows you to show or hide messages from the content process by setting or clearing the checkbox labeled Show Content Messages (error 1260877).

JavaScript debugger

  • You can now Search in all files in the current project from the debugger by pressing Shift + Ctrl + F (Windows or Linux) or Shift + Cmd + F (macOS) (error 1320325).

Network monitor

  • The Network monitor request list now allows you to block a specific URL (error 1151368).
  • You can now resend a network request without editing the method, URL, parameters, and headers, using the Resend command on the context menu (error 1422014).
  • The context menu of the Network monitor Headers tab now allows you to copy all or some of the header information to the clipboard in JSON format (error 1442249).

Page inspector

  • A button has been added to the rules panel of the Page inspector that allows you to toggle the display of any print media queries (error 1534984).
  • The fonts panel now includes a slider to modify letter-spacing (error 1536237).
  • A warning icon appears next to unsupported CSS properties or rules that have invalid values, to help you understand why certain styles are not being applied (error 1306054).

Storage inspector


  • The Accessibility Inspector now includes a new Check for issues feature, which will include a number of audit tools to highlight accessibility problems on your web pages. The first available check is contrast, for highlighting color contrast problems.
  • The preference that controls the visibility of internal extensions (system add-ons and hidden extensions) on the about:debugging page has been changed from devtools.aboutdebugging.showSystemAddons to devtools.aboutdebugging.showHiddenAddons (error 1544372).
  • Responsive design mode has been redesigned — the Device Settings dialog (device selection menu > Edit List...) is now more intuitive and simpler to use (error 1487857).



  • The <track> element — represented by HTMLTrackElement (en-US) — now receives a cuechange (en-US) event in addition to the TextTrack itself, if the text track is a contained by a media element (error 1548731).
  • <link> elements support the disabled attribute again, albeit with different behavior. When disabled is set on a <link> element along with rel="stylesheet", the referenced stylesheet is not loaded during page load, and will be loaded on demand when the disabled attribute is changed to false or removed (error 1281135).





No changes.



CSS Object Model (CSSOM)


DOM events

Media, Web Audio, and WebRTC



  • The HTTP Clear-Site-Data (en-US) header no longer supports the executionContexts directive. This was removed due to problems with interactions between interconnections among different kinds of data at different points in the navigation process and the way the specification is designed. It has been proposed that this directive be removed from the specification for this reason, among others (error 1548034).


  • The Content-Security-Policy directive require-sri-for is no longer supported due to concerns about its standardization status. It was previously available only behind a preference, which was off by default (error 1386214).


No changes.

WebDriver conformance (Marionette)

Bug fixes

  • If WebDriver:SwitchToWindow changes the selection to a different window it now waits for its focus and activate events before returning (error 1335085).
  • Fixed the TypeError: this.tabModal is null failure, which sometimes appeared when interacting with modal dialogs or user prompts (error 1538782)


  • Disabled the feature to force unloading background tabs on low memory conditions, to prevent top-level browser contexts from magically disappearing (error 1553748).
  • Disabled priviledged content processes that caused HTTP authentication dialogs not to appear when navigating to a website after opening a new tab (error 1558763).


No changes.

Changes for add-on developers

API changes

  • The The proxy.register() and proxy.unregister() functions have been deprecated and will be removed from Firefox 71 (error 1545811).
  • When an add-on attempts to add a bookmark folder to the root folder, the resulting error message is now much more intuitive (error 1512171).
  • The promise returned by browser.tabs.duplicate() now resolves immediately, before the tabs are completely loaded, to improve performance (error 1394376).
  • Support has been added for, allowing web extension settings to be implemented via enterprise policy (error 1230802).
  • There is now a Group Policy option to blacklist all extensions except the ones that have been whitelisted (error 1522823).

Manifest changes

No changes.

See also

Older versions