There should no longer be a log file. Nifty keylogger stores captured keys via the chrome.storage.local API.

Firefox no longer supports write access to individual files of a user's profile. I am bound to rely on the chrome.storage.local API instead. I suppose chrome.storage.sync instead of chrome.storage.local yields some sort of upload. That API still is a long way from remote access to a file with the logs.

Thank you for your feedback.
As for kltext.txt, mozilla quantum no longer supports direct access to the file system through javascript. That is why I nifty keylogger now stores the log in a local storage object "storedkl". Its content are accessed through the shortcut K.
As for address bar capturing, are you sure previous versions provided this functionality? The issue here is that document.addlistener("keypress") relies on a document. Unfortunately, the address bar is not a document.

Thank you for your proposal. I need to think of how technically
to implement the clipboard.