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DevTools support for cross-site iframes with Fission is in progress and this page summarizes the current state.

The DevTools team is listening in in the room on Mozilla's Matrix server.

Instructions for enabling Fission for DevTools:

  1. In about:config, set the "fission.autostart"
  2. Restart the browser

You can file DevTools Fission related bug in Bugzilla, here.

See detailed testing results (gdoc)

See also Fission Project wiki page

Fission Compatibility

Known issues are split into two milestones (M2 and M3).


Summary of known issues related to DevTools panels.


The Accessibility panel should be fully compatible with Fission.


  • M3 Service Workers coming from remote frames are not displayed (bug 1473257).


  • M2 New Fission compatible Performance panel will be enabled (by default) at the end of October (bug 1668218).


  • M2 Basic support for highlighting elements in the page when inspecting their CSS properties and box model (bug 1623667, bug 1572654)
  • M3 Advanced features related to highlighting elements in the page. This includes support for highlighting grid elements, shapes defined using CSS clip-path property, highlighting fonts, geometry editor for absolute positioned elements within relative positioned elements and inspecting CSS animations (bug 1568827)
  • M3 Search within the Inspector panel doesn't included remote iframes (bug 1568880)
  • M3 Eydropper (a button in the Inspector's panel toolbar ) used to grab a color from the page (bug 1568831)


The Console panel should be fully compatible with Fission.



  • M2 Sources coming from remote frames are not listed in the Sources side-bar (bug 1659969)
  • M2 Breakpoints should work as expected including those in `onLoad` scripts
  • M3 Debugging of service workers should work as expected
  • M3 Special breakpoints set for: DOM mutation, XHR, various DOM events, Logpoints and Watchpoints should work as expected.

Style Editor

  • M2 Stylesheets coming from remote frames are not available (Bug 1664941).


  • M2 Show all data coming from remote frames: Cookies, Session & Local storage, Extension storage, IndexDB and Cache data (bug 1644192)


  • M3 Memory usage of remote frames is not displayed.


  • M3 Objects coming from remote frames are not displayed.

Miscellaneous Features

Summary of known issues related to independent features.


  • M3 Screenshot doesn't work with remote frames (bug 1568833)

Service Workers

  • M3 Support for Service Workers is not not compatible with Fission.