There is an official mozilla project called "electrolysis" which is about rebuilding FF so that every tab runs in a single process. The idea and goals are described here:
To rebuild FF like that is a huge effort, because so much has to be changed fundamentally. Mozilla had some other ideas, to improve Firefox's response times more easily. Thats why the electrolysis project has been freezed.
I think current FF versions already include some of those other improvements. Don't know if they are complete. AFAIK the electrolysis project is still freezed.
click_to_play may be an alternative to noscript: http://www.h-online.com/open/news/item/Firefox-14-introduces-HTTPS-search-by-default-Update-1644075.html
And this is about current improvements in FF's memory mamagement for plugins and sandboxes: http://www.h-online.com/open/news/item/Firefox-15-reduces-memory-consumption-1649125.html
P.S.: I would like to add that IMHO starting many processes will consume much memory. Sometimes there are ways to reduce this consumption, but they are not always applicable. I don't know about the total memory consumption, but Chromium does at least consume much more swap space than Firefox on my Linux system.