Firefox has Memory issues. If the browser is kept open for a while, even if I close all tabs except one Firefox doesn't clear the memory that it occupied. In my case I kept the browser open for more than a day; 2 windows with 4 tabs each. From the second day onwards it takes up more than 512Mb of memory and even typing becomes slow.
I found this article that explains how to fix the memory leak issue in firefox. Its basically tuning for better performance.
Hope this helps you.
