Very quick test here. Results might be of interest.
Page: http://maxforums.org/threads/opera_browser_firefox/0004.aspx
IE8 (32 bit) : 2 processes totalling about 41MB.
Chrome (regular release) : 3 processes, totalling approx 50MB.
FF (4B12) : 1 process, total approx 65MB.
Obviously depends which ads & images get loaded so not an exact 1/1 match.
Best regards,
Steve Williams
Director
Advance Software Limited