Mark,
If you installed WildFire! by dragging it into your "My Widgets" side-bar panel, just open the "My Widgets" panel again, locate the icon for WildFire!, right-click it and choose "Remove".
You can also do it from the File menu:
File -> Application -> Application Management.
Highlight WildFire (in the Applications list) and then click the "Uninstall" link.
HTH
Mat