Beware: Not direct google search Rated 1 out of 5 stars
This add-on installs a URL that goes to a Standard8 domain, not directly to Google. I would suggest following the manual instructions on the MozillaZine KB article. Removing it did seem to restore things properly.
I've just re-downloaded the current version of the add-on, nothing in the add-on except for its ID mentions standard8. I don't see how this can redirect to any standard8 domain.