MyTabs is a designed for the person that uses there browser tabs as micro-bookmarks. When the browser doesn’t have a specific set of resources available at all times, you start feeling like something is missing. Not only do you care about having those resources open in a tab, but you also like them in a certain state (ie. logged in to..).
You should now have everything you need to create all those tabs when Firefox opens, but also to create new tabs and build the steps required to get you back where you want to be.