Für alle, die den RAM-Verbrauch von Firefox etwas reduzieren wollen, hätte ich hier genau das richtige 
http://forums.mozillazine.org/viewtopic.php?t=354828
man muss noch was wichtiges dabei beachten
Large Images are Not Compressed
When Firefox displays images it decompresses them. When combined with memory cache and Fast Back/Forward (bfcache), this can cause pages with large or many images to make the browser use a lot of memory. This is not a leak, because when the memory is not required it gets released to the heap.

http://forums.mozillazine.org/viewtopic.php?t=354828
man muss noch was wichtiges dabei beachten
Large Images are Not Compressed
When Firefox displays images it decompresses them. When combined with memory cache and Fast Back/Forward (bfcache), this can cause pages with large or many images to make the browser use a lot of memory. This is not a leak, because when the memory is not required it gets released to the heap.