Remove the Proxy URL Configuration from Firefox

Click on the icon Open menu in the top-right corner of Firefox.
Then click Options to open the configuration page.
Select the Advanced from the left-side list.
Then select the Network tab.
Then click Settings... in order to open the next window.
Select the option: No proxy
Click OK to finish the configuration.
Open our detection page and check that DNSProxy is no longer active on your computer.