email - Multiple thunderbird users using same local directory

I have two users "tramp" and "office" on my desktop, and I want to run thunderbird from both users(I trust both users). I dont have enough disk space, so I want both the users to use the same local directory. Is this possible?

I googled and found two solutions, but both dont seem to work:

--> solution 1 with users "default" and "newbie"

sudo addgroup default-thunderbird
sudo usermod -a -G default-thunderbird default
sudo usermod -a -G default-thunderbird newbie

cp -R ~/.mozilla/thunderbird ~/.mozilla/thunderbird.backup
chgrp -R default-thunderbird ~/.mozilla/thunderbird
chmod g+rw ~/.mozilla/thunderbird
find ~/.mozilla/thunderbird -type d -exec chmod g+x \{\} \;

And then, with Thunderbird not running, newbie could run:

mv ~/.mozilla/thunderbird ~/.mozilla/thunderbird.old
ln -s ~default/.mozilla/thunderbird ~/.mozilla/thunderbird 

The above solution gives me a permission error and even if I change permissions, the settings are not picked up.

--> solution 2

gksu -u default thunderbird

The command just exits without opening thunderbird and without giving any error.

Thanks in advance,