(edit v1.4.1)
Simplified UI for adding engines, defaults to directly adding engines to ContextSearch and prompts for installing OpenSearch engines via the API
-------------------------------------------

The api isn't 3rd party. It's mine written specifically for this add-on. It just happens to be hosted on google's app engine with a generic name.

(edit) It probably could stand to be simplified a bit for novice users. The complexity comes from attempting to integrate with Firefox's One-Click search engines. If I kept it simple with bookmark keywords, the search engines wouldn't be added to the OpenSearch engines in the search toolbar. Adding OpenSearch engines requires an external URL, so the api is necessary. I'll look into adding a simple/advanced option that bypasses all OpenSearch integration and just adds to ContextSearch