"Notice that most of these tips only free up some memory at the expense of (usually) loading speed for web pages. You won't make Firefox 10 times faster, but you will surely make it use less RAM.
"Tweak the browser.sessionhistory.max_total_viewers variable
In Firefox, open a new tab (Ctrl+T) and type about:config in the address bar. Click on the I'll be careful, I promise! button and start typing the variable name browser.sessionhistory.max_total_viewers in the Filter text box."
