it is not fixed wired into the code. You can change it in "overlay.xul" in your plugin-directory under \chrome\content\overlay.xul
In that file search for "keyset" then you should find two key-entries there.
There you can change the attribute keycode to seomthing else.
List of keycodes are listed here : https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Tutorial/Keyboard_Shortcuts
The modifiers attribute tells if you have to press additional buttons. See link above it is mentioned there what values can be set.
Save your changes and restart the browser, after that the new shortcut should work in theory.
Have to admit did not try it myself but i am quite sure it works that way
It is very technical so i hope you can work with my instructions given so far.
In case you do not know what to select you could tell here what key-binding you like and we tell you how to adjust the setting.