I wondering how to configure the JSRuntime at best. There are many parameters for JS_NewRuntime(), JS_NewContext(), JS_SetGCParameter(), JS_SetGCParameterForThread(), ... Are there some guidelines or recommendations ?
The default options should work fine, I would just make sure that the method JIT is enabled -- this is done through a JS_SetOption that depends on which SpiderMonkey version you're running.
Also check out the JSAPI user guide for example embedding techniques and background information, as well as the JSPI cookbook.