"Firefox is already running" problem on 6.0

[Jesse Sheidlower]

When I try to launch Firefox, I get a message reading "Firefox is
already running, but is not responding. To open a new window, you
must first close the existing Firefox process, or restart your
system."

I do not have a Firefox process running, and restarting the system
(which is not something I generally like doing just to get an app
to start) has no effect. The only FreeBSD-related message about this
that I found talks about deleting lock files in ~/.mozilla, but I
don't have any Firefox lock files. There was a Solaris-related 
discussion of this that advised upgrading, but I'm up to date with
Firefox (running 1.5.0.1,1).

I'm using FreeBSD 6.0-STABLE #3.

Any suggestions? Mozilla runs fine, but I had finally made the shift
to Firefox.

Thanks.

Jesse Sheidlower