If Firefox is started without an Internet connection on Linux (can happen on start up when the wifi isn't connected yet), the browser continues to refuse to connect to all webpages (unable to connect). It needs to be killed and restarted to work. Offline mode is not ticked. If offline mode is manually ticked and unticked it makes no difference. Ticking offline mode and retrying doesn't work and offline mode is automatically unticked. In the current version of OpenSuSE this is happening on every restart (possibly wifi is getting started a bit later), and it is also reproducible if manually started while disconnected from the wifi.