You can read this documentation about this:
http://kmeleon.sourceforge.net/wiki/ConfigFiles#accel
To quit an accelerator, CTRL S in this case, go to menu Edit -> Config -> Accelerators. This open your accel.cfg file in a notepad window.
Add this line at the end of file and save changes for erase a default accelerator as CTRL S;
CTRL S =
If you like, can subs this accelerate to other added other line as for example:
ALT S = ID_FILE_SAVE_AS
or this other:
CTRL ALT S = ID_FILE_SAVE_AS
Remmember restart K-Meleon for changes take effect.
Greetings.
K-Meleon in Spanish