Ars Technica reports that Microsoft has fixed the update status of the Search Enhancement Pack and posted instructions to remove the extension from Firefox

Microsoft has fixed the distribution scope of a toolbar update that, without the user's knowledge, installed an add-on in Internet Explorer and an extension in Firefox called Search Helper Extension. Microsoft told us that the new update is actually the same as the old one; the only difference is the distribution settings. In other words, the update will no longer be distributed to toolbars that it shouldn't be added to. End users won't see the tweak, Microsoft told Ars, and also offered an explanation on what the mystery add-on actually does.

  Microsoft explains mystery Firefox extension, fixes update