no longer able to open web pages using Firefox browser

I have recently (today) installed a device (Mini Wireless USB adapter) on my desktop computer. I am now connected to my ISP modem wirelessly. I have been using Firefox as my browser for many years (ten?) and have not had a problem until today. When I attempt to go to a web site I get a notice that says: "Unable to find the proxy server. Firefox is configured to use a proxy server that can't be found. Check the proxy settings to sure they are correct. Check to make sure your computer has a working network connection. If your computer or network is protected by firewall or proxy make sure that Firefox is permitted to access the web."

I am able to get to any web site I choose when using another browser. I am also receiving my emails, and able to send emails. So I know the computer has a working network connection. When I have visited the Mozilla support site (having to use another browser) I see advice that shows opening the Settings page and getting to the Proxy settings. When I open my "Settings" page from the menu on the Firefox home page upper banner I do not see any option to get the Proxy settings. How do I access the Proxy settings page? Or how do I access the Firewall settings? Don't forget, I cannot open any web page from Firefox.