If you absolutely need to do this (I don't know what for, though), you can press Insert+3 to pass the keystroke through to the application one time.
If you need to disable JAWS find permanently:
- While in Internet Explorer, press Insert+8 to go to the JAWS Keyboard manager.
- You'll land in the list of applications. Press Tab to go to the list of scripts.
- Locate IEFind which is the script name for Ctrl+F.
- Press Del to remove the keystroke.
- Confirm the removal, save your changes and exit Keyboard manager.