Yes, you need keyword.enabled set to false otherwise Firefox will still search even though you have a different search box :(.

In Firefox, it is also possible to set keyword.enabled to false and still search explicitly in the url bar via the keyword search mechanism (they overloaded the terminology a bit :/, the one if you right click on a search box and select "add a keyword for this search"). I've been thinking of trying to just use DDG style ! keywords via the url bar (and s for a default search to make it easier to type, maybe single letters would be easiest in general) rather than a search box. OTOH, the keyword search (the second type :/) seems neglected and I wouldn't be surprised to see it disappear at some point.