Mozilla's Firefox 3.0 browser uses memory much more efficiently than its rivals, according to an independent tester who wrote a memory-monitoring utility to track usage by Firefox, Internet Explorer (IE), Flock, Opera and Safari.

In a lengthy post to his Web site, .Net developer Sam Allen spelled out the data he collected from the "Memory Watcher" application he wrote specifically to track Web browser memory use.

Although Allen acknowledged that the testing was unscientific -- he ran each browser between 2.69 hours and 2.91 hours, for instance, and didn't claim to have visited the exact same pages with each -- he claimed that the trend lines drawn by Memory Watcher were valid. The results, he said, "Are not a direct comparison in any way, but they offer a visualization of trending in the memory behavior of the layout engines and interfaces."

Firefox 3.0 was the clear winner, not only because it used the least amount of memory of any of the tested browsers, but its memory use didn't noticeably grow over time. "This browser exhibits memory usage that is by far lower than the others," Allen said of Firefox 3.0. "It releases memory to the system and the trend line is nearly flat."

The poorest marks went to Apple's Safari 3.1 for Windows -- Allen tested only the Windows versions of each browser -- which consistently consumed more memory the longer it was used. "Safari on Windows shows extremely poor memory management," he said.

Other browsers, including Microsoft's IE 8 Beta 1, Flock Inc.'s Flock 2.0 and Opera Software ASA's Opera 9.5, were in the middle, memory management-wise, he argued. While their memory use crept up over time, the increase was much more gradual than Safari's. "IE did well...although a worrying trend in the data could indicate that it[s memory usage] would keep escalating," Allen said.

Browsers are regularly dinged for "memory leaks," the term used to describe the increase in memory use the longer an application is used. In some cases, the memory load becomes big enough to degrade the overall performance of some computers.

Older versions of Firefox, including Firefox 2.0, for example, were assailed for rampant memory leaks, criticism that drove Mozilla to reduce the browser's memory footprint in the just-released Firefox 3.0.

Allen did not immediately reply to an e-mail Friday asking for further comment on his memory tests.