Dynamic results don't work properly right now when they declare themselves as heuristics. I'm filing this a few months after I originally meant to, so I don't remember the details, but IIRC the problem is that there's no heuristic group for them, so they end up being classified as UrlbarUtils.RESULT_GROUP.HEURISTIC_FALLBACK. That's not a problem by itself; the problem is that there's always some other heuristic result that ends up winning. Now that I think about it, I'm not sure what happens when there are two fallback heuristics. I think the first one wins.

The obvious fix is to add a heuristic group for dynamic results. It would have a high priority. I haven't thought enough about whether that's a good idea.

This came up because both Daisuke's unit converter and Dale's calculator use dynamic results that should be heuristics but it didn't work. (We ended up giving them suggestedIndex = 1.)