When you are browsing, it happens frequently when you find an interesting link that you want to visit but in order to do that you have to stop reading the current page.
TABU is an extension for the Mozilla Firefox browser, which ensures that you do not leave a link without visiting. For this, it uses a list of "not visited pages" which you can manage in a variety of ways.
A small perspective among them, where you will still see the smallest page view. Others display a date date, similar to the one before, but with a calendar embedded page, by date they are added to the list.
All these TABAs are an excellent navigation tool that makes installing valuable.