"In Opera 12.16 I can make any search engine the default.
Nope, that possibility was removed in that very version (12.16), to stop rogue sites/code from hijacking Opera users default search engines (You can only set the ones provided). The last version of Opera (Presto) to support setting any search engine as a users default is 12.14"
Thanks for clarifying. Actually 12.16 preferences still pretends to allow you to set any engine as the default, but evidently doesn't execute the preference any more! I guess I hadn't used the facility since 12.14. I'd still prefer to use ixquick, of course, since it seems not to want to steal my soul.
Tim