Ref: http://www.alfredforum.com/topic/5993-custom-searches-with-full-url-as-the-query/
Unless {query} is the entire URL, the Open URL action behaves as if {query} is a query string value and URL-encodes it, i.e. it assumes:
http://www.example.com/page?arg={query}
This is not always the case, however. {query} may also be a part of the URL path, e.g.
http://www.example.com/{query}/some/other/thing
In the latter case, most browsers will choke on the URL (I think only Firefox is smart enough to handle URL-encoded paths). Alfred should ideally provide a checkbox to turn URL-encoding of {query} off to avoid messing up {query}. Alternatively, it could try to determine whether {query} is actually the value of a GET parameter (for example, based on the presence of "arg=…"), but the on/off option is probably more robust.