For myself, I use K-Meleon for precisely the reasons you like it. It is efficient. However, you might consult this page:
http://kmeleonbrowser.org/forum/read.php?1,72013 in case you want to modify K-Meleon to do some extra things that you might require in the future.
As for FireFox - there is a value that can be put in about:config that won't fix the memory leaks but might bring memory under control. When you minimize K-Meleon it releases memory substantially. The same can be done for FireFox. Type about:config into the url bar and then create a new BOLEAN value (right click on what you see) and type config.trim_on_minimize and set it to true. This won't cure the usage, but at least when you minimize Firefox, it will return some memory.
If you want a practical demonstration of how efficient K-Meleon is to its Mozilla brothers, go to something like NFL.com on a Sunday, click on a team that is playing. This will set up a graphic football field which is updated constantly. Have both browsers (K-Meleon and any other Mozilla browser) running at the same time for that page, then bring up the taskmanager (CTRL-Shift-ESC) and watch the memory usage build.