Make sure FireFox is up to date.
Suppose you wish to make the location to Los Angeles
Connect your VPN to a server from this location
Visit the Firefox Add-on page and install Location Guard
Once the installation is completed, click the Location Guard extension icon in the browser.
Select Options. This will open the options menu in a new tab.
In the left-side menu, click Fixed Location.
7. Move the location marker to match the location of your VPN server
8. Return to the webpage you want to access. Refresh the page and click the Location Guard extension icon.
9. In the list of options, select Set level for {web page name}
10. Select Use fixed location and close the extension menu.
11. Check that your location has changed.