What's new to share today is that the Generational GC is now enabled by default in the latest Firefox nightly builds. The change was finally accepted to turn on the "GGC" for desktop versions of Firefox.
Unfortunately, the Generational GC isn't fully polished yet. Some users are reporting big increases of memory use for Firefox with the new collector. One OS X user reported the start-up memory use being up by 14MB (8%), with 50 tabs open the memory use is up by 117MB or 9%, and after closing the 50 tabs the memory use was up by 35MB or 8%. See the aforelinked bug report for more details. With follow-up testing, however, the results appeared to be more positive.
Look for the Generational GC by default in future versions of Firefox (v31) and stay tuned for more information and testing.