An anonymous reader writes "This experiment graphs the memory usage of Chrome and Firefox 3.5 (along with Safari and Opera) over a series of 150 Web page loads using an automated script. Firefox 3.5 shows the lowest memory usage in all categories, including average memory usage, maximum memory usage, and final memory usage. Chrome uses over 1 GB of memory due to its process architecture. Safari 4 and Opera show memory usage degradation over time, while Chrome and Firefox 3.5 are more reliable in freeing memory to the OS."
IE 8 was not included "because the author could not find a way to prevent it from opening a new window on each invocation of the command."