diff --git a/browser/chrome/nfstream.js b/browser/chrome/nfstream.js
index 33c3f6b..dc3afd5 100644
--- a/browser/chrome/nfstream.js
+++ b/browser/chrome/nfstream.js
@@ -13,9 +13,6 @@ If not, see <http://www.gnu.org/licenses/>.
 ------------------------------------------------------------------------------------------------------------------------
 */
 
-var success_count = 0;
-var error_count = 0;
-
 function upload_to_nfstream(msg) {
     chrome.storage.local.get({export_port: '28314'},
                               function (items) {
@@ -27,9 +24,8 @@ function upload_to_nfstream(msg) {
                                                   true);
                                          xhr.setRequestHeader("Content-type", "application/json");
                                          xhr.send(JSON.stringify(msg));
-                                         success_count++;
                                    } catch (e) {
-                                         error_count++;
+                                         // ignore
                                    }});
 }
 
diff --git a/browser/firefox/nfstream.js b/browser/firefox/nfstream.js
index 2936b2b..befa71e 100644
--- a/browser/firefox/nfstream.js
+++ b/browser/firefox/nfstream.js
@@ -13,9 +13,6 @@ If not, see <http://www.gnu.org/licenses/>.
 ------------------------------------------------------------------------------------------------------------------------
 */
 
-var success_count = 0;
-var error_count = 0;
-
 function upload_to_nfstream(msg) {
     browser.storage.local.get({export_port: '28314'},
                                function (items) {
@@ -27,9 +24,8 @@ function upload_to_nfstream(msg) {
                                                    true);
                                           xhr.setRequestHeader("Content-type", "application/json");
                                           xhr.send(JSON.stringify(msg));
-                                          success_count++;
                                     } catch (e) {
-                                          error_count++;
+                                          // ignore
                                     }});
 }
 
diff --git a/nfstream/system.py b/nfstream/system.py
index c5a1800..05e7b77 100644
--- a/nfstream/system.py
+++ b/nfstream/system.py
@@ -86,6 +86,7 @@ class RequestCache(OrderedDict):
     @staticmethod
     def get_nearest_request_idx(requests, flow):
         """ return from a list of requests the nearest request to a flow based on timestamp and a grace time period """
+        nearest = None
         if requests is not None:
             grace_time = 1000
             # grace time period: we are matching a flow to a request identified by remote ip and creation timestamp
@@ -98,9 +99,8 @@ class RequestCache(OrderedDict):
                     min_time_diff = time_diff
                     min_time_diff_idx = idx
             if min_time_diff <= grace_time:
-                return min_time_diff_idx
-            else:
-                return None
+                nearest = min_time_diff_idx
+        return nearest
 
     def match_flow(self, flow):
         requests = None
@@ -168,17 +168,15 @@ class ConnCache(OrderedDict):
 def get_conn_key_from_flow(f):
     """ compute a conn key from NFlow object attributes """
     if f.protocol == 6:
-        return 6, \
-               min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
-               min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
+        k = 6, min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
+            min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
     elif f.protocol == 17:
-        return 17, \
-               min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
-               min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
+        k = 17, min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
+            min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
     else:
-        return 0, \
-               min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
-               min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
+        k = 0, min(f.src_ip, f.dst_ip), max(f.src_ip, f.dst_ip), \
+            min(f.src_port, f.dst_port), max(f.src_port, f.dst_port)
+    return k
 
 
 def match_flow_conn(conn_cache, flow):
@@ -196,18 +194,19 @@ def match_flow_conn(conn_cache, flow):
 
 def get_conn_key(c):
     """ Create a 5-tuple connection key tuple """
+    k = None
     if c.raddr != () and c.pid is not None:
         src_ip = c.laddr.ip
         dst_ip = c.raddr.ip
         src_port = c.laddr.port
         dst_port = c.raddr.port
         if c.type == SocketKind.SOCK_STREAM:  # TCP protocol
-            return 6, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
+            k = 6, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
         elif c.type == SocketKind.SOCK_DGRAM:  # UDP protocol
-            return 17, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
+            k = 17, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
         else:  # Non TCP/UDP mapped with 0 as protocol Id
-            return 0, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
-    return None
+            k = 0, min(src_ip, dst_ip), max(src_ip, dst_ip), min(src_port, dst_port), max(src_port, dst_port)
+    return k
 
 
 def system_socket_worflow(channel, idle_timeout, poll_period):
diff --git a/nfstream/utils.py b/nfstream/utils.py
index 02b39fd..06deb97 100644
--- a/nfstream/utils.py
+++ b/nfstream/utils.py
@@ -36,10 +36,11 @@ def process_unify(proc_name):
     """ unify browser process names across platforms """
     proc_name = proc_name.lower()
     if proc_name == "chrome":
-        return "chrome"
+        proc_name = "chrome"
     else:
         if proc_name == "geckomain":
-            return "firefox"
+            proc_name = "firefox"
+    return proc_name
 
 
 def validate_flows_per_file(n):