Assuming that your Windows partition is mounted as /mnt
and that your Windows username is hey
, first copy the (randomly named) old profile directory to your Ubuntu account:
cp -r /mnt/Users/hey/AppData/Roaming/Mozilla/Firefox/*.default ~/.mozilla/firefox/win7profile
Then quit Firefox and edit the ~/.mozilla/firefox/profiles.ini
file, changing StartWithLastProfile=1
to StartWithLastProfile=0
and adding the following to the end:
[Profile1]
Name=win7profile
IsRelative=1
Path=win7profile
Restart Firefox. It should then allow you to select which profile you want to use.