This page allows you to install an OpenSearch Description File for the CrossRef Metadata Search back-end (aka "SIGG") that powers several CrossRef citation plugins. To see how this works, browse to this page using the FireFox browser and then click on the popup menu near the search box in the top-right of your browser window. This popup should give you the option to "Add CrossRef Metadata Search" (see picture below).
This, in turn will set your default search to use the SIGG search back-end. Try a search like "renear text really" and you will get back two citations. After you experiment with this, remember to set your preferred search engine back to whatever you use as a default!
Finally, please note that this is merely an OpenSearch Description file. The system does not yet support OpenSearch Response or any other of the many cool OpenSearch features that Tony Hammond has been implementing at Nature and discussing on the CrossTech blog. These features may appear later.