Tracing the memory leak: Is it Firefox 3?

Yesterday, we mentioned that we've been noticing recent versions of Firefox, including 3.0.5, have exhibited the memory leak problems that used to plague Firefox 2. We are noticing this on both Windows XP SP3 and Vista SP1.

We'd also noticed that systems where the add-on Tab Mix Plus was installed, did not appear to exhibit the same memory leak. Today, we uninstalled Tab Mix Plus (reluctantly, because we like it) from one system. On that system, the memory use pattern has changed, perhaps moderated, though we're not sure the leak has gone away. It now appears to be slower than in our tests yesterday, and from time to time, something in Firefox does clean up parts of memory from time to time. In one test, we had two Firefox windows open with seven tabs open in one of them, a dozen in the other -- a pretty full slate. Task Manager is showing us that Firefox grabs memory in one-megabyte chunks per second, for about a minute at a time, and then leveling back out to about 300,000 KB.

So if it's not a leak right now, at least it's a fight, and we'll let you know what else we find.