Somewhat tangential, but I think that many of the difficulties they are facing with Electrolysis and this whole multi-process movement is that, in older version

Somewhat tangential, but I think that many of the difficulties they are facing with Electrolysis and this whole multi-process movement is that, in older versions of FF, everything is so tightly integrated. IIRC, Firefox has(had?) a lot of old code written long before modern concerns were even fathomed; addons back-in-the-day had access to the entire process-- every tab, all the DOM, and everything shared the same namespace (shady calls from webpages were blocked somehow, not sure if it was true sandboxing or not), so AMO mods would block addons (or updates) that didn't adhere to their namespacing policy. I'd bet a lot of that integration is still there, and most of what we're seeing is the result of what is probably a very messy untangling.