Mozilla to Bring Chrome-Like Site Isolation Feature for Firefox Users


  • Mozilla started work on Project Fission in April this year
  • Now, the company has started work on Fission MemShrink
  • It looks to reduce RAM usage in content processes

Google introduced a feature called Site Isolation with Chrome 67 to mitigate the Meltdown and Spectre vulnerabilities that came to light earlier in the year. Mozilla reportedly started work on a similar feature back in April itself, but now the company has launched a new project that will improve RAM usage in each content process, in order for site isolation to work well. Mozilla is calling its site isolation feature as Project Fission, and its RAM usage improvement as Fission MemShrink. Project Fission, just like Chrome’s Site Isolation, looks to prevent attacks that happen between processes and sites, by restricting sharing of processes between multiple sites. Google rolled out Site isolation for Windows, macOS, Linux, and Chrome OS users this July.

Bleeping Computer got hold of a Mozilla official email, which confirms the beginning of Fission MemShrink – a project which essentially looks to use less memory in content processes. The company is aiming to reduce memory usage by at least 7MB on all platforms. “In order for site isolation to work, we need to be able to run at least 100 content processes in an average Firefox session. Each of those processes has its own base memory overhead – memory we use just for creating the process, regardless of what’s running in it. In the post-Fission world, that overhead needs to be less than 10MB per process in order to keep the extra overhead from Fission below 1GB.”

“Right now, on our best-cast platform, Windows 10, is somewhere between 17 and 21MB. Linux and OS-X hover between 25 and 35MB. In other words, between 2 and 3.5GB for an ordinary session. That means that, in the best case, we need to reduce the memory we use in content processes by at least 7MB. The problem, of course, is that there are only so many places we can cut memory without losing functionality, and even fewer places where we can make big wins. But, there are lots of places we can make small and medium-sized wins,” the company notes in the mail.

As mentioned, Mozilla does not guarantee whether it will succeed in reducing RAM usage, but effort towards it has begun. As it’s still a work in progress, there is no timeline for the launch of Project Fission. However, you can see Fission MemShrink’s headway here.