User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:50.0) Gecko/20100101 Firefox/50.0 Build ID: 20161129173726 Steps to reproduce: When my corporate VPN client reconnects, Firefox can't open any pages. Actual results: Page not found when trying to refresh a page or opening a new tab. Expected results: Firefox should notice this and work.

Some additional information: Environment: - Firefox 50.0.2 - Using a proxy ("Use system proxy settings") - Using Cisco AnyConnect VPN 3.1.14018 When the VPN disconnects and reconnects, Firefox is not able to show any pages. I usually do the following to fix it: 1. Options->Advanced->Network Settings->Select "No proxy"->Press "OK" 2. Select "Use system proxy settings" again 3. Firefox works again... The behaviour is similar to https://bugzilla.mozilla.org/show_bug.cgi?id=1245210

Does switching to work offline and back fix the issue too? Could you please provide logs of both cases? I.e. one log containing VPN reconnect only followed by one failed page load, second log containing VPN reconnect + resetting proxy settings followed by one successful page load? See https://developer.mozilla.org/en-US/docs/Mozilla/Debugging/HTTP_logging use MOZ_LOG=timestamp,rotate:200,nsHttp:5,nsSocketTransport:5,nsStreamPump:5,nsHostResolver:5,proxy:5

This is dup of 1321841. I will take a look at logs from other bug in coming days.