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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


  • M2 Q4 2020
  • M3 Q1-Q3 2021
  • MF Future


Summary of known issues related to DevTools panels.


The Accessibility panel should be fully compatible with Fission.


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


  • MF New Fission compatible Performance panel is enabled in Nightly and Beta. It yet needs to be enabled in Release (bug 1693316).


  • MF 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)


The Console panel should be fully compatible with Fission.



  • MF Debugging of service workers should work as expected
  • MF 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


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


  • MF Memory usage of remote frames is not displayed.


  • MF Objects coming from remote frames are not displayed.

Miscellaneous Features

Summary of known issues related to independent features.

Service Workers

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