Fission is Mozilla's project to implement Firefox site isolation. This introduces a major architecture change in Firefox such that a unique process is allocated for the main web page and for each unique third-party iframe embedded in it, thereby safely sandboxing them and further strengthening Firefox security.
The Fission team is standing by, ready to answer your questions in the #fission:mozilla.org room on Mozilla's Matrix server.
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.
- Some extensions might not work fully. But please file bugs if you find an extension that doesn't work!
- Cross-site iframes appear empty when printed.
- Cross-site iframes appear empty in screenshots.
- Documents with cross-site iframes cannot enter the BFCache.
- Session history is not tracked for cross-site iframes.
- Session restore occasionally fails to restore page state, such as page zoom, scroll offset, or form data.
- DevTools support for cross-site iframes with fission is incomplete.
- Attempting to debug extensions or workers from a non-fission window can cause crashes.
- Linux resource exhaustion issues with large tab counts, including:
- Excessive memory usage
- File descriptor exhaustion issues
- X11 connection exhaustion on Linux (bug 1635451)
Fission is still in active development, and can only be enabled in Firefox Nightly.
- In about:config, set the "fission.autostart" and "gfx.webrender.all" prefs to "true". DO NOT edit any other "fission.*" or "gfx.webrender.*" prefs.
- Restart Nightly.
You can verify that Fission has been enabled by hovering over a loaded tab. If the tooltip contains a "[F]", Fission is enabled.
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.
To disable Fission, reset the "fission.autostart" pref back to "false" and restart Nightly.