another instance of firefox is already running

Another update. another F-up. Every time I try to open a (web-)link from an outside program (mail, excel, ...) I get a popup telling me "another instance of firefox is already running. Please close other instances of firefox before launching mozilla firefox, portable edition". If I completely ignore the popup (=leave it open), en click the SAME link a second time, it is opened in firefox portable. But that requester remains open till I click it . So: opening a weblink is now a "please click three times, because FF does not like users" thing? Any solution ideas? I am getting soooo frustrated with this...

( 88.0.1 (64-bit) )