Yes. You will have to save them to another drive, usb key or CD/DVD. The Firefox
settings are in a hidden folder in your home folder /.mozilla/firefox.. Save the
entire folder or browse the profile which will have a bunch of random
alphanumerics followed by.default. Thunderbird's settings are in a hidden folder
called .thunderbird with a similar alphanumeric.default. Inside will be your
address book and mailboxes. It may be under .mozilla-thunderbird, depending on
how it was installed.

To see either hidden folder you will have to enable hidden files by clicking on
View and then on Show Hidden Files or press Ctrl+H.

Once they are save to the media of choice then just copy then back after you
have re-installed Ubuntu. If they don't work then just use each program once and
it will set up a new profile and then copy over all the subfolders from your
backed up copies into the new profile.