A website reports that Firefox is outdated, incompatible or not supported - see How to reset the default user agent on Firefox.See Firefox and other browsers can't load websites for some troubleshooting suggestions. This is probably a problem with your Internet connection. Any changes you've made will automatically be saved. If you don't connect to the Internet through a proxy (or don't know whether you connect through a proxy), select No Proxy.The Connection Settings dialog will open. In the General panel, go down to the Network Settings section.Click the menu button and select Settings. Click the menu button and select Options Preferences. In the Menu bar at the top of the screen, click Firefox and select Preferences. To check your connection settings in Firefox:
See Enter proxy server settings on Mac at Apple Support for more information on proxy settings. If you connect to the Internet through a proxy, compare Firefox's settings to Internet Explorer's - see Microsoft's guide to proxy settings.