Appears to have been abandoned and the core functionality no longer works. The best similar extenstions I've found are "Open Incognito" and "Temporary Containers".
Hi, I'm the author of this add-on. It is for sure not abandoned. I was surprised to read that it doesn't work for you, as I'm using it every day. Can it be that you didn't allow the add-on to run in Private windows? Unfortunately this is necessary to be able to list private windows and open new private windows. I've just submitted a new version (1.4), which displays instructions how to allow the add-on to run in private windows. Unfortunately - according to my knowledge - this permission can't be requested programmatically.
