I'm not sure what gave me the impression but, in my mind "process-per-tab" and "Electrolysis" were linked, but that was a misconception:

>In great detail, (as of April 2021) Firefox’s parent process launches a fixed number of processes: eight web content processes, up to two additional semi-privileged web content processes, and four utility processes for web extensions, GPU operations, networking, and media decoding.

>While separating content into currently eight web content processes already provides a solid foundation, it does not meet the security standards of Mozilla because it allows two completely different sites to end up in the same operating system process and, therefore, share process memory. To counter this, we are targeting a Site Isolation architecture that loads every single site into its own process.