This extension is not compatible to recent versions of Firefox and is no longer maintained.
You should uninstall it. Click in the menu on "Tools -> Add-Ons", switch to the "Extensions" tab at the top of that window, then scroll down until the entry "Search Engine Ordering" appears. Click on it. After that, buttons will appear that let you (amongst other things) uninstall it. Do that!
For questions on the extension there are threads at the Forums of MozillaZine and firefox-browser.de. (There is also one at TEM but in order to have all informations available at one place and to avoid doing the same work over and over again I prefer MozillaZine.)
Questions and other Messages targeted directly at me can be sent as an EMail.