All the incognito browser windows share the same “session” in Firefox. So say you open an Incognito window to browse Facebook or something, then you open another Incognito window, this new incognito window is linked to the previous incognito window, meaning you are logged into Facebook at that new Incognito window as well. This is because, as I explained before, all the incognito windows share the same “session”
The only way to clear incognito window is to close ALL of them and then create a new incognito window. You dont have to close the main non incognito Firefox window though, just close all the incognito windows. Then open a new one, now your previous session is destroyed and you are new again.
You may know it but its not that common knowledge as it should have been
They don’t allow addons, and probably some other things.
But I honestly would take clearing my session every time. I use a bunch of different services, and having those sessions preserved is really convenient, and 2FA is quite annoying if I had to do 10x logins/session (or more!). I just checked, and I have >20 services in my MFA app, and there are others that are SMS/email/their app only.
So I use private browsing when I know I want my history cleared, I use containers to group things by account, and I use the regular non-containerized session for casual searches and whatnot. I only need to do 2-3x 2FA logins/day, and those are mostly for work stuff (VPN and SSO manager) that expires after 4 hours or whatever.