Firefox unresponsive when launching... periodically

periodically when I try and open firefox I will get an error box that says that firefox is already trying to start but is unresponsive and I should close it down or restart my system. Forcing a misbehaving app to quit does nothing... Firefox is not already open and I have to reboot to make it go away..
I have a dell xps 410 machine running dual monitors which share the same desktop.. I run Karmic Koala.
thoughts??

ps I am not sure what precipitates this... I know that when I reboot my firefox automatically opens to ubuntu one which fails to recognize my machine and wants me to relog in and re-add my computer... not sure if that is related or not though...