Firefox high memory consumption is one of the biggest challenges this popular, open-source project, has faced in tough browser wars, while there have been quite a few attempts to make the web-browser optimized with forks and utilities and Mozilla foundation even addressed the "memory leakage" issue with targeted efforts like MemShrink - the results were promising but nothing very exciting.
Enter "Firemin" - the free, handy, little, portable application which magically shrinked my Firefox memory usage times within seconds (see comparison picture below) of launching. You simply launch the application and it eliminates all Firefox memory leaks, including the one's caused by extensions.
Firemin uses a safe API function called EmptyWorkingSet that basically forces the process (in this case Firemin) to use less memory. Other words, tells Firefox to give back some of the system memory it’s hanging on to. Using this function will sometimes result in a slight performance decrease measured in milliseconds , but I do mean slight, the chance of you noticing the performance decrease is almost zero.
The software is small and portable, I would strongly recommend you give this a try.