Firefox and Limewire Eating Up My RAM

So one day I was happily surfing the Internet, but felt a sudden, violent urge to check my CPU memory usage. What do I find? This:

Now, LimeWire, I understand. I remember, when I was still working as a Technical Support Representative, we used to advise customers to avoid using file-sharing programs such as LimeWire, because they could eat up memory, in addition to bandwidth. But Firefox? THE Mozilla Firefox? The world’s number one browser in terms of usability?