I doubt if this is the right place for this kind of question, But I don't know where else I should ask this. If there is a better place to ask this please tell me. I want to create a `webapp` that has sensitive data on it. I want to put that on a usb and be able to run it on every machine with FF without relying on extra extentions/tweaks to the browser. The `webapp` itself therefore can use html/js/css/etc. The data itself will be stored in a lose data file. I want to auto save changes to this file. Temp saving it in a cookie/indexedDB is not an option. So saving it in the normal way isn't an option. The download popup would drive me nuts. I've read some stuff about the fileSystem api and Mozilla's alternative DeviceStorageAPI. Neither seem like an option. IndexedDB is no option because it saves data to the browser. Is there a way to save a file without prompt? Or any other way to accomplish what I want to do? A few of the sources I've red. https://hacks.mozilla.org/2012/07/why-no-filesystem-api-in-firefox/ http://caniuse.com/#search=filesystem https://developer.mozilla.org/en-US/docs/WebAPI/Device_Storage https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API