User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:22.0) Gecko/20130418 Firefox/22.0 Build ID: 20130418112607 Steps to reproduce: 1. Make sure there's an existing non-private Firefox window open. 2. Run "firefox -private-window somefile.html" Actual results: A new private window opens at about:privatebrowsing and the provided file/URL is opened in a new tab in the non-private window. Expected results: The provided file/URL should have either opened in the new private window or not opened at all. I prefer the former since scripting "chromium --incognito-mode <URL> ..." is the last reason I keep Chrome around aside from testing web pages.