I haven't seen quite that symptom, but perhaps I can help.

First, let's see if your Thunderbird profile is still there. Open a Nautilus
window ("Places" | "Home Folder"), and select "View" | "Hidden Files". Browse
around for a folder named ".thunderbird", or possibly ".mozilla-thunderbird".
(Note the initial dot in the file name.)

Most likely, your profile folder will still be there, with some name of the form
" .Default User".

Next, start a terminal window ("Applications" | "Accessories" | "Terminal"), and
enter the command:

thunderbird --profilemanager

You should get a small dialog box that will allow you to select your profile.
See if that gets you back to normal operations.