They've started getting more serious about it. One of their big new JavaScript performance features, type inference, was backed out as soon as they realized it causes significantly increased memory usage -- and it won't get back in until it slims down, despite significant JS performance benefits. In the past, many features slipped in with memory problems and weren't noticed for months or years.

Umm, the claim wasn't speculative, it was measured on an aurora release that you can test out right now: http://www.mozilla.com/en-US/firefox/channel.

I smirked at the headline when I saw it and I came here to say the same thing ... Every release they promise that firefox will use less memory ... hasn't happened yet AFAIK.

The Aurora channel, which is the code that will soon become Firefox 7, has some pretty big memory improvements.

Nicholas Nethercote is leading Firefox's memshrink effort and shared the results so far: http://blog.mozilla.com/nnethercote/2011/08/09/firefox-7-is-...