Useful and needed in modern web browsing to separate your personal data out of big brothers.

这简直就是我用firefox的唯一原因，这个插件太棒了

Very convenient to automatically open each of my websites in its own containers as defined in the configuration.

Excelente! Facilita muito meu trabalho, pois utilizo varias contas ao mesmo tempo

So far the best browser feature! And it's optional in form of extensions. Just take my money!