When I load Firefox, all I get is an error that says: "Your Firefox profile cannot be loaded. It may be missing or inaccessible."
I only installed it today, this was the first time I've tried it. I tried the Profile Manager, and got the same error.
Did you use Firefox before?
Do you have a file profiles.ini ?
If you have a file profiles.ini then try to delete or rename the file profiles.ini to make Firefox create a new default profile.
See also this page if you have used Firefox before.