In the past I’ve started my Firefox with many open Tabs. The negative Side from that, is that this eats many RAM. But now I’ve found the ultimate Firefox Extension for that. The Name of this Extension is “TooManyTabs”. First of all you have to define Categories.
In my Case i have defined the Categories: Work, openSUSE, Blogs and Social Network. The Tabbar shows like this:
There you can find the active Tabs. On the left Side you can find that:
You have one selected Category, but you can set three or four visible Categoriebars. The Best thing now is, that you can “pin” unneeded Tabs into the Categorie Tab. The Result is, that only the active Tabs using the RAM. If you need an Tab later, you can just klick on it and the Tab is active. AFAIK the unneeded Tabs into the Categories Tab are just freezed, and you can use it without Relogin.
If you are on a site, who you would like to add into the Categories Tab. you just have to right-click on the Site, then “Send to..” and you have to choose your Category.
That’s it. Try it out. I like it 
