To resolve the issue of NaturalReader not reading and producing no sound on your PC while using Firefox, follow these actionable steps:

1. Check Your Audio Output:
- Ensure that your speakers or headphones are plugged in and functioning.
- Right-click on the speaker icon in the taskbar and select "Open Sound settings." Make sure the correct output device is selected and not muted.

2. Verify NaturalReader Settings:
- Open NaturalReader and navigate to the "Settings" or "Preferences."
- Check that the sound output settings are configured correctly. Look for options related to audio or voice settings.

3. Test Firefox Sound:
- Open different tabs in Firefox (like YouTube or a music site) to ensure that sound is working in the browser itself. If sound is muted or not functioning in Firefox, you might need to troubleshoot Firefox settings.

4. Clear Firefox Audio Cache:
- Close all Firefox tabs and restart the browser.
- Go to Firefox’s menu (three horizontal lines) > "Options" > "Privacy & Security."
- Scroll down to "Cookies and Site Data" and click "Clear Data" to clear stored data, which could be affecting audio playback.

5. Check Firefox Extensions:
- Some extensions can interfere with audio playback. Go to the Firefox menu > "Add-ons and Themes" and disable any unnecessary extensions, especially those related to audio or media playback. Restart Firefox afterward.

6. Check for Conflicting Software:
- Restart your computer in Safe Mode to see if an extension or background application is causing the sound issue. If audio works in Safe Mode, then a conflicting application might be the cause - learn more.

7. Update Firefox:
- Ensure you have the latest version of Firefox. Go to Firefox menu > "Help" > "About Firefox" to check for updates.

8. Reinstall NaturalReader:
- If the problem persists, consider uninstalling and then reinstalling NaturalReader. This can resolve issues related to corrupted files or settings.

9. Run the Audio Troubleshooter:
- On Windows, search for "Troubleshoot settings" in the start menu, then select "Additional troubleshooters" and run the "Playing Audio" troubleshooter to identify any underlying issues - learn more.

By following these steps, you should be able to resolve the issue of NaturalReader not reading or producing sound on your PC using Firefox. Make sure to test each step to identify where the problem lies.