The directory hierarchy in GNU/Linux is somewhat different to what you
might have been used to in Windows. There is no C: or D: drive, instead
the filesystem starts at the root node, /, then every directory (folder)
is followed by another slash (/ — as opposed to a backslash on Windows).
Thus, what would be C:\\Program Files\\Mozilla\\Firefox\\firefox.exe
on Windows, is usually /usr/bin/firefox on GNU/Linux, and what
would be C:\\Documents and Settings\\Users\\jean\\My Documents\\
on Windows is just /home/jean on GNU/Linux. Much simpler!
If you want to learn a bit more, read the Filesystem Hierarchy Standard
article on Wikipedia, or better yet, enter man hier in the terminal.