Firefox memory footprint

Firefox is releasing one new version after the other. And each new version, Mozilla claims to have enhanced memory usage to reduce the amount of resource required to load each page. Is that a valid claim?

As a curious computer engineer, I decided to install several legacy Firefox versions and compare the amount of memory required to load two greedy pages: and

Here are the results.

One observes that at Firefox 3.6, reading emails from gmail suddenly doubled memory usage. And from Firefox 4.0 on, it requires the triple of memory. I suspect that gmail also loads more content on newer versions since Firefox enhanced javascript support.

But a similar behavior also happened for news journal, although not as intense as for gmail: memory has grown nearly 3 times!

Although the results are no scientific measures, I believe that they show the greedy memory consumption tendencies from Firefox, and that probably Mozilla was not really successful to “enhance memory usage”.