[SWLUG] Backup Backup then Upgrade Ubuntu!

[ilyan]

I had Evolution handling one email address I did not use, and
Thunderbird handling the email address I did use.

Then I did an upgrade, clicked to say to keep the setup I had.  But have
lost the Thunderbird.   "Failed to execute child process Mozilla
Thunderbird ("no such file or directory")" comes up when I click on the
little black square that now appears where Thunderbird used to be.
Though now I seem to have turned that black into a tray on a spring.

Is that likely to be a fatal loss of back emails and addresses?   any
suggestions for recovery? 

Evolving

Ilyan