Yes you can by selecting the Custom Installation option during installation. But the vast majority of Firefox (drive space wise) will be in the user / "roaming" folderset area on the same drive that the operating system is installed on - the C:/ drive. That is the default area for the Firefox Profile.

https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

After installation you can create a new Profile, on a different drive, for your Firefox data and customizations.

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Before you use Chose folder for a custom location you need to create the folder and select that specific folder when you create the new Profile. If you don't or accidentally use the root folder, you could risk losing everything on that drive, so you need to use a new, empty folder when you specify where you want the new Profile.

And once you create the Profile, in the custom location, don't "clean up" what remains on the C:/ drive from the original installation. You will need the profiles.ini file so that Firefox knows where your "in use" Profile folder is located.

Or use Firefox Portable and install it where you want it. "Portable" doesn't follow Windows "convention" for storing "user" files. "Portable" keeps all Firefox files in the same location as where the user installs Firefox. The main short coming is that you would need to install Firefox Portable for each Logon User Account on that PC, if you are using multiple LUA's.

http://portableapps.com/apps/internet/firefox_portable

See also:

• https://developer.mozilla.org/Command_Line_Options

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile