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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).

  • M2 Q4 2020
  • M3 Q1 2021


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).


  • M3 New Fission compatible Performance panel is enabled in Nightly. It yet needs to be enabled in Beta (bug 1693314).


  • 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)


The Console panel should be fully compatible with Fission.



  • 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.
  • M3 When there are several frames from various origins, sources will be missing for some of the origins in the source pane (bug 1659969)
  • M3 Search across all processes (bug 1577878)
  • M3 Debugger doesn't work properly if page loads two remote iframes from the same domain (bug 1503499, bug 1678741)

Style Editor

The Style Editor panel should be fully compatible with Fission


  • M3 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.

Service Workers

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