Comment 27 for bug 294187

I think it is fixed. Otherwise see below:

You can copy my "patch" above** in
your profile directory. In Ubuntu it
is somewhere down that road:
/home/username/.mozilla/firefox/profilename*/searchplugins/
You have to use ctrl+H to show
hidden files and directories and
you can even copy profiles from
Ubuntu to Windows and vice versa.

*profilename=A weird assortment of
letters and numbers.

**to download right click:
"Just the patch for the german Wikipedia searchplugin could not test it"
and choose "save as" and type in
the name "wikipedia-de.xml".
Make sure you turned off the hide
 known file extensions if you try it
in Windows.
To do it open a Explorer Window
and choose "Tools"->
"Folder options..."->View->
uncheck "Hide extensions for known file types".
:)
Extensive Help!