I have always used a separate partition/drive for Data as well as having a separate partition for my home folder. I have now upgraded to Ubuntu 11.04 and I found none of my profiles run under Classic Ubuntu or Unity. They still run perfectly if I use the 'straight' Firefox 4 firefox-mozilla-build from the Ubuntuzilla PPA.
The error message is:
Firefox cannot use the profile "??????" because it is in use. To continue, close the running instance of Firefox or choose a different profile.
This message is apparently given if the profile is locked or if the profile can not be found. It is clearly not a stale lock file as it occurs when you try to create a new profile so it would seem firefox cannot find or has access blocked to the Profile.
I have narrowed the problem down even further and my existing profiles will run in the default location ~/.mozilla/firefox or in a sub-folder below that location. I can also create new profiles in the same locations but not elsewhere.
I have edited profiles.ini to see if it is related to the IsRelative addressing and that is not the cause as one can change a relative to absolute location without problems.
I am baffled. Is this a bug in the modifications for Unity compatibility or a security feature which can be enabled/disabled? Any advice would be much appreciated.