You can choose the program folder location using the full, offline installer (available here) by doing a custom installation. See Custom installation of Firefox on Windows for details.

However, files associated with the Firefox profile will be located in the C-drive AppData folder by default... but you can later create a new profile in a different location. See and Profiles - Where Firefox stores your bookmarks, passwords and other user data and Profile Manager - Create, remove or switch Firefox profiles

In addition to the above reply, the files that register extensions (profiles.ini and installs.ini) are always located in the main profile folder location in AppData\Roaming, but you can create the actual profile that uses only one profile folder for the main root files and for the temporary caches by using "Choose folder".
Note that you should never use a folder for the profile folder that already stores other files (i.e. always create a new folder).