Open a new tab and type "about:config", without quotes, and hit enter. Right-click anywhere on the page, and select New, and then Integer. A box will appear, and in it you should type "browser.cache.memory.capacity", without quotes, and hit ok. Another box should then pop up, and in it you should type the maximum memory you want to allow firefox to use. I suggest 32mb, so type in "32000" without quotes. You can set this to whatever you want based on your browsing needs. For 64mb type "64000", you get the idea. Hit enter, and restart Firefox. Your memory leak is now fixed.