Fission is the Mozilla's project to implement Firefox site isolation: third-party iframes will be loaded in separate processes, safely sandboxed from the web page's content process. The primary motivation is to protect against side-channel attacks like Spectre and Meltdown.

Contact

The Fission team is standing by, ready to answer your questions in the #fission channel on Matrix.

Reporting Bugs

To file a Fission bug in Bugzilla, click here to use this Fission bug template. Or file a bug and include the word “Fission” in the bug summary. The Fission team’s bug triage will find the bug, regardless of which Bugzilla component you file it in. Or

• Fission meta bug 1451850

Known Issues

• Some extensions might not work fully. But please file bugs for any of these issues!
• Some DevTools issues debugging Fission tabs
• Some video player issues on YouTube and Twitch
• Session restore does not restore page zoom level.
• Duo 2FA passcode input may not work, but Duo Push works correctly.

Enabling Fission

Fission is only supported in the Firefox Nightly channel and requires WebRender be enabled!

How to enable Fission:

1. Enable the "fission.autostart" and "gfx.webrender.all" prefs in Nightly. Do not mess with any other "fission.*" or "gfx.webrender.*" prefs!
2. Restart Nightly.
3. Fission should now be enabled. To verify it's enabled, mouse over a tab and look for "[F]" (i.e. Fission) in the tab's tooltip popup.
4. When Fission is enabled, you can open a non-Fission window using the "File > New Non-Fission Window" menu item. This is handy for testing whether a bug is specific to Fission or not.
5. To disable Fission, reset the "fission.autostart" and "gfx.webrender.all" prefs to "false" and restart Nightly.

Milestones

Sub-pages

• Memory
• FrontEnd
• Enabling Tests with Fission
• Fix out-of-process uses of DocShell tree and nsIDocShellTreeItem