Firefox has a new profiles experience in v138 and up. Each can have its own extensions and settings. If you've got more than one you can switch in the taskbar. The only thing you might be missing is using multiple profiles at once?

Have you looked into Firefox Multi Account Containers? I use this extension to quickly switch between multiple tab groups, some of which do use SSO while using the same service (e.g. Outlook). Plus, you can easily create new tabs like Ctrl + Shift + (#1-9) to open a container of your choice among other shortcuts. I know it doesn't meet all your criteria, but each tab group has its own colour and/or icon to make them distinct, while being in the same window