Hello,

A Firefox version you downloaded (a Microsoft Store version) keeps its files in a different location. To start Firefox:

1. Open Microsoft Store.
2. Open Mozilla Firefox product page (e.g., type "Firefox" into the search bar at the top and select Mozilla Firefox from the results).
3. Click the Open button.

Alternatively:

1. Type "Firefox" in the Windows Search Bar at the left bottom of your screen.
2. Select Firefox from the results.

Regarding the error, looks like you are trying to use an old shortcut for your old Firefox version. If so, you can just delete it as it is not needed anymore. For instructions on creating a new one, see these Microsoft answers.

I tried the above 2 ways to open Firefox. Using the search bar I get the same results. Windows cannot find C:\Program Files\Mozilla Firefox\firefox.exe. Make sure you typed the name correctly, and then try again.

Going to Microsoft Store, finding Mozilla Firefox, clicked on OPEN, nothing happens.

Ok, let us check then if an old Firefox version was truly removed, or you just deleted some of its files (in that case, it still virtually exists for Windows and may cause the old paths usage).

1. Open System Settings (e.g. by typing "Settings" in the Windows Search Bar).
2. Select Apps.
3. Type "Firefox" in the search bar above the app list.

How many Firefox instances do you get in the results? If there are at least two of them, I would appreciate a screenshot.