how does per tab incognito work in chrome ? I can only find per window (which i assumed was the only way to do it)
It's not even per-window. If you open an Incognito window and log into a website, any other Incognito windows will share that same cookie jar and thus also be logged in to said website. I would love a way to keep them distinct, but simply opening a new window won't do it--you have to close all Incognito windows/tabs to clear its temporary cookie jar.
Aha, you're right (I don't use Chrome, so I was just assuming the GP was more up-to-date than me on its current features).
I recall Opera 12 had per-tab incognito - I'm not sure, do any current browsers have it?
So Firefox seems to be just jumping ahead of that initial limitation from the start here.