View source for 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 [https://chat.mozilla.org/#/room/#fission:mozilla.org Mozilla's Matrix server].

= Reporting Bugs =

To file a Fission bug in Bugzilla, [https://bugzilla.mozilla.org/enter_bug.cgi?product=Core&bug_type=defect&short_desc=%5bFission%5d&blocked=fission-dogfooding 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}}
* [https://bugzilla.mozilla.org/buglist.cgi?classification=Client%20Software&classification=Developer%20Infrastructure&classification=Components&classification=Server%20Software&classification=Other&f1=cf_fission_milestone&resolution=---&o1=anywordssubstr&query_format=advanced&v1=M4.1%2CM5%2CM6 All bugs blocking Fission Nightly]

= Known Issues =

* Some extensions might not work fully. But please file bugs for any of these issues!
* Some video player issues on YouTube and Twitch. ({{bug|1619370}}, {{bug|1620341}})
* 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.
* Resource exhaustion issues with large tab counts, including:
** Excessive memory usage
** File descriptor exhaustion issues
** X11 connection exhaustion on Linux

= 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 =

{| class="wikitable"
|-
! 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
|}

= Sub-pages =

* [[Project Fission/Memory|Memory]]
* [[Project_Fission/FrontEnd|FrontEnd]]
* [[Project_Fission/Enabling_Tests_with_Fission|Enabling Tests with Fission]]
* [[Project Fission/DocShell_Tree_Replace|Fix out-of-process uses of DocShell tree and nsIDocShellTreeItem]]