Where is Ubuntu storing installed programs?

I am using Ubuntu and when I click on a program to download Firefox asks me "What should firefox do with this file?" And in the "Open with" I would like to find a program "Package installer". The problem is - I don't know where to look for. Where is the program stored (I installed it using Ubuntu Software Center)

They are usually stored in the following folders:

/bin/
/usr/bin/
/sbin/
/usr/sbin/

If you're not sure, use the which command:

~$ which firefox
/usr/bin/firefox

If you installed the package with the Ubuntu package manager (apt, synaptic, dpkg or similar), you can get information about the installed package with

dpkg -L <package_name>

Simply, type the command:

~$ whereis "program name"

for some applications, for example google chrome, they store it under /opt. you can follow the above instruction using dpkg -l to get the correct naming then dpkg -L to get the detail.

hope it helps

Just for an addition reference to the above answers. I can not use dpkg -L to find the correct path for cuda. See the results I got from dpkg -L

$ dpkg -L cuda
/.
/usr
/usr/share
/usr/share/doc
/usr/share/doc/cuda
/usr/share/doc/cuda/copyright
/usr/share/doc/cuda/changelog.Debian.gz

the correct path is /usr/local/cuda

$ ll /usr/local | grep cuda

lrwxrwxrwx  1 root root    8 Oct 20 18:45 cuda -> cuda-9.0/

drwxr-xr-x 15 root root 4096 Oct 20 18:44 cuda-9.0/

Btw, I did install cuda by the command of

dpkg -i xx_cuda_xxx.deb

to find the program you want you can run this command at terminal:

find / usr-name "your_program"

If you are looking for the folder such as brushes, curves, etc. you can try:

/home/<username>/.gimp-2.8

This folder will contain all the gimp folders.

Good Luck.

If you are using google-chrome it might be inside your chrome extension, you can just remove the extension and use the downloaded & updated version (ubuntu 20.04)