Summarize the following:
You should end up with the settings app open on the Apps & features screen. Scroll down untill you find an app named "Mozilla Firefox" and click on it. If prompted with a User Account Control prompt, click "Yes". If you are ready to uninstall Firefox, click "Next" and click "Uninstall" to remove Firefox from your Windows 10 PC. Click "Finish" to close the uninstallation wizard. Some files or folders may not be removed by the uninstall and will have to be deleted manually. In particular, you may want to delete this folder: C:\Program Files\Mozilla Firefox .

Summary:
Click the search button and type in "Apps and features" and click on "Apps & features". Once you click on it, click on "Uninstall" and if prompted, click on it again to begin the uninstallation wizard. The uninstallation wizard for Firefox should show up. If you would like to tell Mozilla why you uninstalled Firefox, you may click on the box next to "Tell Mozilla why you uninstalled Firefox". Remove other files and folders associated with Firefox.