One of the better features in new browsers is the ability to open all your tabs from your last session. But it’s also a hassle when they start loading all at once, sucking away precious memory.
You can stop this, making sure all tabs are idle until you need them. To do so in Firefox, head to the Options Screen, and then stay on the General Tab.
There, under the “Startup” options, you’ll see a box next to the words, “don’t load tabs until selected”. Click on that, and you’ll make sure those tabs won’t drain away any memory until selected.