Firefox 69 for developers

This article provides information about the changes in Firefox 69 that will affect developers. Firefox 69 was released on September 3, 2019.

Changes for web developers

Developer tools


  • Event Listener Breakpoints let you diagnose which code a page executes in response to browser events. You can pick specific types, such as click or keydown, or whole categories of events, like all mouse input events. (Firefox bug 1526082).
  • Scripts shown in the debugger's source list pane can now be saved via the Download file context menu option (Firefox bug 888161).
  • In the debugger's source list pane, loaded extensions are listed with their name, rather than just their UUID (Firefox bug 1486416), making it much easier to find the extension code you want to debug.
  • The debugger now loads significantly faster via lazy-loading scripts (Firefox bug 1527488).




  • When you hover over an element in the Page Inspector, the infobar that appears now includes the fact that an element is a flex container, or flex item (Firefox bug 1521188).
  • When inspecting a page containing a grid with a subgrid, the parent grid's overlay lines are displayed whenever the subgrid's lines are displayed; if the parent grid's overlay checkbox is unselected, then its lines are translucent (Firefox bug 1550519).

Remote debugging

  • For our mobile web developers, we have migrated remote debugging from the old WebIDE into a re-designed about:debugging, making the experience of debugging GeckoView on remote devices via USB much better (Firefox bug 1462208).



  • In order to align more closely to the specification, the text track associated with a <track> element no longer loads the WebVTT file containing the text cues if the element is created in its default disabled mode. To access or manipulate the cues when the mode is disabled, change the mode to either started or hidden; this will trigger loading of the WebVTT data (Firefox bug 1550633).


  • The HTML <keygen> element has been removed from Firefox. It was deprecated some time ago, and its purpose has generally been supplanted by other technologies (Firefox bug 1315460).






New APIs


Media, Web Audio, and WebRTC


WebDriver conformance (Marionette)


  • Marionette now dynamically handles the opening and closing of modal dialogs and user prompts (Firefox bug 1477977), which also means that multiple open prompts will be handled (Firefox bug 1487358).
  • Tracking protection and DOM push features are now disabled by default to avoid the removal of parts of the DOM, and extra notifications (Firefox bug 1542244).
  • Automatic unloading of background tabs if Firefox runs into a low memory condition is now disabled — this badly interacts with automation when switching between tabs (Firefox bug 1553748).

Changes for add-on developers

API changes

Other changes

See also

Older versions