http://billmccloskey.wordpress.com/2013/12/05/multiprocess-f... "The total memory usage for multiprocess Firefox is only 10MB greater than single-process Firefox. We should be able to shrink this difference with some effort"

As for the excess memory usage on chrome, "OneTab" might help https://chrome.google.com/webstore/detail/onetab/chphlpgkkbo... (It's available on Firefox) https://addons.mozilla.org/en-US/firefox/addon/onetab/