Brilliant! So there is basically no need to add plugins like this one (http://news.ycombinator.com/item?id=3035153) - currently on the front page of HN - so long as you are ok with launching new incognito windows.
That's what I used Opera for before I deleted my FB account. Safari is currently the browser I use only for my real Google account activity (Gmail, Calendar and G+ only).
I know there are solutions like http://br.mozdev.org/multifox/ , but they have never worked quite as I wished.