JavaScript write to file?

[Cintaria]

I'm writing an extension for FireFox and part of it requires writing to a local file (part of the extension). So my question is, do you want some toast? hehe, RedDwarf xD Anywho - how do I write to a local file in JavaScript?

[Puratech]

I think the main problem is varied security settings mean its not entirely reliable to expect users to allow the javascript that much access to write to the file system. For settings or a small bit of info, consider saving that in a cookie.

Also, google is your friend.
javascript write to file - Google Search