Zim - It is under 'Settings -> (Advanced) - > Keyboard Commands (or Shortcuts'.
Open that up - and you SHOULD be able to delete the commands individually by the bs-del method. Painful to go thru them all- and my suggestion really was tongue-in-cheek. I am not using the standard browsers (FF,GoolagChrome,IExploder) any longer- so you may or may not be able to disable individual shortcuts.
On the OS- not sure- and I don't really recommend it.
When one's mouse goes out, you gotta be able to navigate somehow - even if to only shut-down the 'pooter legitimately.