It’s not you. Amazon removed the option to buy Kindle books directly through apps and even limits it in some browsers. On Firefox, it should normally still work, but sometimes ad-blockers, privacy settings, or outdated cookies stop the “Buy” button from working. Try clearing your Amazon cookies, disabling any extensions temporarily, or using Chrome/Edge just to test. If it works there, then it’s a Firefox compatibility issue. Worst case, you can always buy the Kindle book from Amazon’s main website on desktop, and it will still sync to your Kindle app or device.