It would be perfect if… Rated 4 out of 5 stars
It would be perfect if:
1. the new shortcuts were shown in menus – for example I set Ctrl+J for Downloads, but the tools menu shows the default shortcut Ctrl+Shift+Y (Linux);
2. the preferences part was added to in-content preferences too;
3. it was possible to define new shortcuts.
Ziegen is right, custom shortcuts doesn’t work in Private mode (FF 22). It may be related to #1.