An anonymous reader writes: As promised, Mozilla today announced the release of Firefox OS Simulator 4.0 with a focus on developers who want to make money in the Firefox Marketplace. You can download the new version now for Windows, Mac, and Linux from Mozilla Add-Ons. First and foremost, the new simulator supports test receipts for paid apps: each app’s dashboard features a drop-down menu where you can select a receipt type. Choosing one of these will have the simulator add-on downloading a test receipt from a Marketplace receipt service and reinstalling the app using it. This lets developers test receipt verification with whatever receipts types they may require (valid, invalid, and refunded).