But both Parmenter and Schroepfer denied that Mozilla had suddenly gotten memory "religion" and had only recently dedicated resources to the issue. "We've been working on this for a long time," Parmenter said, countering questions by some who have asked what took Mozilla so long to decide memory leaking was a problem. "[Memory] has always been important in the back of peoples' minds, even in the early days. In Firefox 2.0, there was definitely a trend toward smaller memory." But Mozilla hesitated to implement memory reductions in Firefox 2, he said, because it was already in production.
Schroepfer chimed in. "We've been investing in [memory consumption work] for quite a while, and some changes have been worked on for more than a year. What you're seeing now are the final results of that work."
Last November, after Christopher Blizzard, a member of Mozilla's board, tied reducing Firefox's memory consumption to the push to put the browser on mobile handsets, it seemed work intensified on plugging leaks. And earlier this week, Schroepfer noted that performance improvements in Firefox 3.0 would carry over into the move on mobile.
"We're really excited about how this looks in mobile, but we would have done it anyway," Schroepfer said Friday. "We wanted to do it on the desktop."
Parmenter created the memory test -- he dubbed it a "stress test" -- that loaded 29 different pages through 30 windows in 11 cycles, for a total of 319 page loads. At the end, all tabs but one were closed and the browser allowed to "sit for a few minutes" to see how much, if any, memory the system reclaimed.
Although Parmenter and Schroepfer ran both Apple's Safari browser (and the in-development nightly builds from the WebKit project) and Microsoft's Beta 1 of Internet Explorer 8, but both were unable to finish, crashing at various places. Opera's 9.5 Beta, code named "Kestrel," however, was able to complete the tests.
"[Opera] peaks around 240MB and doesn't free up any memory at the end, so ends at 240MB," said Schroepfer in a comment to Parmenter's original blog, the Opera test prompted by numerous readers' requests. "Performance during the run is similar to Firefox 126.96.36.199 but higher than Firefox 188.8.131.52 at the end. It is significantly higher than Firefox 3, which peaks around 220MB and ends at 85MB."
Parmenter admitted that the test was just one of any number of possible benchmarks, and said Mozilla would be coming up with other tests. "I don't think we're done in memory," he said. "We need more tests to show more usage patterns. We need to find tests where we don't look as good [as the one published]."
And there is more memory work that can be done, Parmenter said. "I don't think we're done in memory. There's additional work to look at how we handle caches, for example."
Firefox 3.0 Beta 4, which was released last Monday, can be downloaded for Windows, Mac OS X and Linux in 36 languages from Mozilla's site.