Had a problem with Firefox first after trying to update my profile and got this same message. Struggled to get rid of it, deleted, reinstalled, deleted, rebooted Laptop about 10 times before I finally got it to install and then went back into Thunderbird and got the same message "Your Thunderbird profile cannot be loaded. It may be missing or inaccessible." I didn't do anything to Thunderbird. Was working fine. I can't get rid of the error message and back into it. I had Thunderbird all setup with my email accounts!!!! What a waste of time.