--- a/toolkit/devtools/security/socket.js
+++ b/toolkit/devtools/security/socket.js
@@ -162,17 +162,28 @@ let _getTransport = Task.async(function*
 let _attemptTransport = Task.async(function*(settings) {
   let { authenticator } = settings;
   // _attemptConnect only opens the streams.  Any failures at that stage
   // aborts the connection process immedidately.
   let { s, input, output } = yield _attemptConnect(settings);
 
   // Check if the input stream is alive.  If encryption is enabled, we need to
   // watch out for cert errors by testing the input stream.
-  let { alive, certError } = yield _isInputAlive(input);
+  let alive, certError;
+  try {
+    let results = yield _isInputAlive(input);
+    alive = results.alive;
+    certError = results.certError;
+  } catch(e) {
+    // For other unexpected errors, like NS_ERROR_CONNECTION_REFUSED, we reach
+    // this block.
+    input.close();
+    output.close();
+    throw e;
+  }
   dumpv("Server cert accepted? " + !certError);
 
   // The |Authenticator| examines the connection as well and may determine it
   // should be dropped.
   alive = alive && authenticator.validateConnection({
     host: settings.host,
     port: settings.port,
     encryption: settings.encryption,