The profile is probably still there; it's just that TB can't find it. First, look in c:\users\(yourID)\appdata\roaming\thunderbird\profiles to identify the right one. There may be more than one, but yours would be the larger one and most recently used. Now, TB looks at c:\users\(yourID)\appdata\roaming\thunderbird\profiles.ini to determine where the profile is located. This is simple text file that can be viewed with Notepad. In it, you will see path statements. All you need to do is edit the ini file with the exact name/location of your profile. It's probably safest to update all path entries. Save the file and TB should run fine. My guess is the update somehow corrupted the ini file.

I had this problem. Thunderbird stopped working. I uninstalled and downloaded and reinstalled and still had this problem. Following the instructions above I found the .ini file had Default = D:\profile . My PC has no D:. Problem solved by replacing that with Path = c:\users\(yourID)\appdata\roaming\thunderbird\profile .