I usually mount /opt to a drive I partition I have with all kind of stuff like my projects etc.
Today I install LMDE, then while creating a shortcut to thunderbird on my top panel I noticed that thunderbird is installed to /opt/thunderbird and /usr/bin/thunderbird is a link ??
shalom@shalom-laptop ~ $ ls -la /usr/bin/thunderbird
lrwxrwxrwx 1 root root 28 Apr 15 08:55 /usr/bin/thunderbird -> /opt/thunderbird/thunderbird
then I noticed that there are other things in /opt like a folder named /opt/kde3 with bin,lib and lib64 under it,
a folder named /opt/debian with some deb files under it, a folder named mint-flashplugin-x64 ,
I wonder how did this happen? I never had the OS installing files to /opt, Usually I have a dual boot where both OS mount this drive to /opt, now my /opt has mint specific files in it.