This (and the other suggestions below) are what I’ve tried previously.

It’s close but Google’s got the native solution and the “window-level” containers that have individual per-container icons make it much easier for me to sort my sessions. Unfortunately it looks like Firefox still has them relegated to a single taskbar item. I guess this is necessary since container tabs can be moved between windows unlike Chrome which draws a hard line between windows. I guess this is just the method Firefox went with but it makes my processes a lot more difficult.

Thanks for the suggestions. I’ll give it another go and check out ungoogled Chromium as well.