Mozilla Firefox has never been good with system memory consumption, the free open-source web-browser is a very well-known memory guzzler thanks to various memory leaks in it's codebase. There have been various un-official solutions to the problem and addons like RamBack do help make things in-control a bit, but nothing works as a concrete solution to the problem which is needed to face-off today's tough competition.
Mozilla developers have now decided to finally address the issue seriously and a dedicated team called MemShrink is now in-operation to tackle the issue.