Additional Firefox windows always starts on the same desktop

Hi List; I have a strange firefox issue. If I start firefox on desktop one (in KDE) and later want to start other instances of firefox from say desktop 2 or desktop3, the desktop always switches back to desktop 1 (or where the first firefox window is opened) and firefox opens there. I can right click on the firefox titlebar and choose "to desktop" to move it. Any thoughts? Thanks in advance...