It's enabled 'by default', but it's still a regular Firefox extension that can be turned off easily. Comment #2 by Alexander Sack reads: Thanks. To workaround

It's enabled 'by default', but it's still a regular Firefox extension that can be turned off easily. Comment #2 by Alexander Sack reads: Thanks. To workaround you can disable the extension in tools -> addons. Later Adam Bielinsky fleshes it out: At the moment, every user on a machine has to click Tools, then Addons, then Extensions, then Multisearch, then Disable, and then restart Firefox.