Reinstalled Firefox. It's not a fresh install. Why?

Your personal information is stored within the following location:

%AppData%\Mozilla\Firefox\Profiles\

When you remove and reinstall Firefox, those files and folders with your profile settings are left intact. Although you actually did successfully replace the Firefox program files, the things that you see are still retained within your Windows user profile.

I saw the same thing happen when the 64-bit version of Firefox was first released. I removed the 32-bit version of Firefox from my Windows 10 Pro x64 machine, and when I installed the 64-bit version of Mozilla's browser it made for a very smooth transition. The following information was still there:

1. Bookmarks
2. Browsing and download history
3. Passwords
4. Open windows and tabs
5. Cookies
6. Web form auto-fill information
7. Personal dictionary

For future reference, should you need to do this again it would probably be a bit faster and easier to utilize the built-in Refresh Firefox feature, instead. In your Firefox address bar enter about:support and then select the Refresh Firefox button on the upper-right:

Sources:
Profiles - Where Firefox stores your bookmarks, passwords and other user data
Refresh Firefox - reset add-ons and settings