When two major vulnerabilities known as Meltdown and Spectre were disclosed by security researchers in early 2018, Firefox promptly added security mitigations to keep you safe. Going forward, however, it was clear that with the evolving techniques of malicious actors on the web, we needed to redesign Firefox to mitigate future variations of such vulnerabilities and to keep you safe when browsing the web!

We are excited to announce that Firefox’ new Site Isolation architecture is coming together. This fundamental redesign of Firefox’ Security architecture extends current security mechanisms by creating operating system process-level boundaries for all sites loaded in Firefox for Desktop. Isolating each site into a separate operating system process makes it even harder for malicious sites to read another site’s secret or private data.

We are currently finalizing Firefox’s Site Isolation feature by allowing a subset of users to benefit from this new security architecture on our Nightly and Beta channels and plan a roll out to more of our users later this year. If you are as excited about it as we are and would like to try it out, follow these steps:

To enable Site Isolation on Firefox Nightly:

1. Navigate to about:preferences#experimental
2. Check the “Fission (Site Isolation)” checkbox to enable.
3. Restart Firefox.

To enable Site Isolation on Firefox Beta or Release:

1. Navigate to about:config.
2. Set `fission.autostart` pref to `true`.
3. Restart Firefox.

With this monumental change of secure browser design, users of Firefox Desktop benefit from protections against future variants of Spectre, resulting in an even safer browsing experience. If you aren’t a Firefox user yet, you can download the latest version here and if you want to know all the technical details about Firefox’ new security architecture, you can read it here.