Fission Site Isolation: Default Enforcement Timeline for Low-Memory Devices Unresolved

Rollout Status and Hardware Constraints

Firefox's Fission architecture has been gradually enabled by default since version 86, controlled via the fission.autostart preference. Mozilla's telemetry-driven expansion continues without a published version target for universal enforcement.

Memory Overhead vs. Security Baseline

Typical memory increases of 10–20% are documented, with out-of-memory risks on devices below 4 GB RAM. Enterprise policies can disable Fission via Group Policy, but no consumer-facing fallback exists for hardware that cannot sustain the process-per-site model.

Open Decision

The unresolved question is whether Mozilla will mandate Fission for all profiles regardless of device capability, or maintain a permanent opt-out path for constrained hardware.

• Will a minimum-RAM threshold be codified into the default rollout logic?
• Is a fission.autostart fallback to non-Fission behavior planned for low-memory detection?
• What telemetry metrics determine the final enablement decision?