NPAPI-SDK is a tiny package providing headers necessary to build NPAPI plugins without the need for emerging whole xulrunner. Migration requires the package to check for npapi-sdk.pc as well as current headers. The pkg-config file doesn't require any additional Mozilla components, and is versioned using NPAPI versions rather than Mozilla versions. Reproducible: Always
So what should we do about this, write us a patch if you want it.
Fixed in live ebuild.