Patrick O'Callaghan
You might consider the Tab Session Manager extension. It periodically (or on demand) saves your current tabs and windows and can restore them again on startup, but optionally not actually load each page until you decide to visit it.
Andras Simon:
I believe that this is the default behaviour of Firefox. I mean the "not actually loading until you switch to it" part. The restore part is not the default, just an option. But neither needs an extension.
I might give the manager thing a try and see what it offers me.
I've noticed the same thing, that when you fire-up Firefox, only the currently selected tab actually loads. Mine is set up to remember and restore the previous session. I do shut down the browser, and log off the computer.
Perhaps other people are leaving their browser running 24/7? I'm not sure what Firefox does with pages on unselected tabs when the browser is always running. I suspect *anything* running on those tabs will keep on running, because I know I can switch away from tabs playing YouTube videos and the sound keeps going. I'm not at all surprised that something bad might romp through all the RAM.