When I was upgraded to Firefox 22, pages refused to load with "Firefox is configured to use a proxy server that is refusing connections." Firefox > Edit > Preferences > Advanced > Settings > Configure Proxies... was set to "Use system proxy settings" but in System Settings > Network > Network proxy, Method is set to "None". It was working fine before the Firefox upgrade. The work-around seems to be to set "No proxy" in Firefox.
When I was upgraded to Firefox 22, pages refused to load with "Firefox is configured to use a proxy server that is refusing connections." Firefox > Edit > Preferences > Advanced > Settings > Configure Proxies... was set to "Use system proxy settings" but in System Settings > Network > Network proxy, Method is set to "None". It was working fine before the Firefox upgrade. The work-around seems to be to set "No proxy" in Firefox.