Project Fission
Fission is 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.
Contact
The Fission team is standing by, ready to answer your questions in the #fission:mozilla.org room on Mozilla's Matrix server.
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.
- Fission meta bug 1451850
- All bugs blocking Fission Nightly
Known Issues
- X11 Windows stability issues when opening many Flash tabs on Linux. bug 1129492
- Some extensions might not work fully. But please file bugs for any of these issues!
- Some DevTools issues debugging cross-origin iframes.
- Some video player issues on YouTube and Twitch. (bug 1619370, bug 1620341)
- Session restore does not restore page zoom level.
- Cross-origin iframes will appear empty when printed.
- Cross-origin iframes may occasionally appear in global history.
Enabling Fission
Fission is still in active development, and can only be enabled in Firefox Nightly.
How to enable Fission:
- Enable the "fission.autostart" pref in Nightly using about:config. No need to mess with any other "fission.*" prefs.
- Restart Nightly.
Fission should now be enabled. To verify it's enabled, load a webpage, hover over the tab, looking for a "[F]" (i.e. Fission) in the tab's tooltip popup.
If you encounter an issue while using Fission, it is possible to open a non-fission window within the same browsing session using the "New Non-Fission Window" item in the hamburger menu. This can be useful to determine if issues are Fission-specific, or to work around fission-specific breakage.
In general, avoid modifying other "fission.*" prefs, as they are often for testing, or unstable features very early in development, and aren't ready to be used for day-to-day browsing.
To disable Fission, reset the "fission.autostart" pref to "false" and restart Nightly.
Milestones
| Milestone | Description | Date |
|---|---|---|
| M1 | OOP iframe framework | 2019-02-28 |
| M2 | Semi-functional OOP iframe | 2019-05-06 |
| M3 | Whistler All Hands demo | 2019-06-26 |
| M4 | 90% of mochitests are passing | 2019-11-12 |
| M4.1 | 100% of mochitests are passing | TBD |
| M5 | Fission is dogfoodable (internal Fx user testing) | 2020 Q2 |
| M6 | Enable in Nightly on desktop (X% rollout) | 2020 |
| M7 | Enable in Beta on desktop (X% rollout) | 2020 |
| MVP | Enable in Release on desktop (X% rollout) | TBD |
| - | Start work on Android Fission | ~2021 |