when i download an email attachment from Hotmail e.g. *.docx it becomes _*.docx_ (with added underscores) of course, my computer will not recognize the file
This only happens in hotmail. If I manually change the file extension after download, everything works. So why is the browser adding the underscores at the beginning of the file name and on the end of the file extension?
Alla svar (1)
It could be one of your extensions interfering with the way Firefox downloads Microsoft Office attachments. Try running Firefox in Safe Mode (https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode) and see if the problem goes away.