Don't try to open the file with another application, but open the xpi file in Firefox via File > Open File

See:

• http://kb.mozillazine.org/Installing_extensions

Ok I opened the file through Firefox, installed it, restarted the browser, yet it did not work. The quick find bar is still there.

Did you try to change the current shortcut keys in the preferences of the extension to something else?

How do I do that?

You need to create or modify an existing user.js file to customize this extension as explained on the home page of the extension.

• http://kb.mozillazine.org/Editing_configuration
• http://kb.mozillazine.org/user.js_file

• http://nic-nac-project.de/~kaosmos/index-en.html#searchkeys

This extension sets as default the key | (for search only in links) and ^ (for normal search).
You can change these settings with the following two preferences:
user_pref("searchkeys.link.key", xxx);
user_pref("searchkeys.find.key", xxx);
where xxx is the ascii code of the key you like for the action.
You can also disable at all the feature, with this preferences:
user_pref("searchkeys.disable.all", true);