What do you mean by "Creating a new gecko-based product"? I might have overlooked something but last time I checked, there was no way to use a current version of Gecko outside of Firefox, except for GeckoView on Android.
I'm not sure what this is (something like FirefoxOS?) but what I meant is there's no such thing as a "Gecko WebView" (for embedding in UI frameworks) or a "Gecko Electron" that you can use without forking some huge Mozilla thing (except for GeckoView).
