Firefox 5 was all about bug stomping and the stillborn channel switcher, Firefox 6 will see the addition of lots of HTML5 and CSS3 features and more privacy controls, and Firefox 7 — at long last — will focus on memory management and performance increases.

Firefox 6, which moves to the Beta release channel today, introduced a significantly improved about:memory page with buttons that can manually trigger garbage collection (GC) and cycle collection (CC). Garbage collection frees up memory by clearing old and unused JavaScript objects; cycle collection does the same for DOM objects, including web pages. By hitting these buttons repeatedly — or by hitting “Minimize memory usage”, which triggers both processes three times in a row — you can reduce Firefox 6’s memory footprint significantly.

In Firefox 7, however, which will feature-freeze and percolate down to the Aurora channel today, there are two big changes that should reduce the memory footprint of Firefox for all users: increased GC frequency, and defragmentation of memory chunks used by various core Firefox processes. Increased GC frequency should massively improve the performance of Firefox over long, multi-day browsing sessions, and less fragmentation will result in memory footprints that are tens or hundreds of megabytes smaller than they currently are.

Of course, for users with 6GB of RAM or more, these changes won’t make a huge difference — but for mom and pop beige-box surfers with only 2GB of RAM, these two fixes will make a noticeable difference to the long-term performance of Firefox. With the memory footprint squished, Mozilla’s attention will now hopefully turn to the desktop implementation of Electrolysis, the technology that separates content and core functionality into individual processes.

Firefox 6 also features instrumentation to help Mozilla identify which parts of Firefox’s interface feel slow, meaning that by the time Firefox 8 rolls around, not only will the browser itself be more efficient but it will also feel faster. As we all know, Chrome isn’t actually a whole lot faster than Firefox, it just feels snappier — something Mozilla no doubt wants to emulate.

If you want to dive in and try out the new reduced-memory Firefox 7, either grab a Nightly build, or wait for it to appear on the Aurora channel later today. Incidentally, if you’re trying to keep up with the new version numbering, tomorrow’s Nightly build will be Firefox 8!

Read more about Firefox’s “MemShrink” efforts