How to configure:
1. Input about:config in the address bar
2. Type changesearchshortcut in the filter box
3. Change extensions.changesearchshortcut.key to whatever key you want
4. Change extensions.changesearchshortcut.modifiers to whatever modifier you want
5. Restart Firefox
The 'key' can be any printable character (even space).
Modifiers can be any of the following: meta, shift, control, accel, alt. If you want multiple modifiers, separate them by comma.
If, finally, Mozilla decides to ship Firefox with CTRL+E mapped to Panorama, you may want to use the Change Panorama Shortcut as well, to avoid any conflicts.
Note: version 0.2 of this add-on will NOT replace the current CTRL+K shortcut for 'search'. It will simply provide another shortcut for it.
If you need something that will simply change the shortcut which is now CTRL+K, get version 0.1 of this plug-in.