diff --git a/netwerk/protocol/http/nsHttpHandler.cpp b/netwerk/protocol/http/nsHttpHandler.cpp
index 0b7d462460ac..0b85dde3a2c1 100644
--- a/netwerk/protocol/http/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/nsHttpHandler.cpp
@@ -365,6 +365,8 @@ nsHttpHandler::Init()
         obsService->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, true);
         obsService->AddObserver(this, "net:clear-active-logins", true);
         obsService->AddObserver(this, "net:prune-dead-connections", true);
+        // Sent by the TorButton add-on in the Tor Browser
+        obsService->AddObserver(this, "net:prune-all-connections", true);
         obsService->AddObserver(this, "net:failed-to-process-uri-content", true);
         obsService->AddObserver(this, "last-pb-context-exited", true);
         obsService->AddObserver(this, "webapps-clear-data", true);
@@ -2044,6 +2046,11 @@ nsHttpHandler::Observe(nsISupports *subject,
         if (mConnMgr) {
             mConnMgr->PruneDeadConnections();
         }
+    } else if (!strcmp(topic, "net:prune-all-connections")) {
+        if (mConnMgr) {
+            mConnMgr->DoShiftReloadConnectionCleanup(nullptr);
+            mConnMgr->PruneDeadConnections();
+        }
     } else if (!strcmp(topic, "net:failed-to-process-uri-content")) {
         nsCOMPtr<nsIURI> uri = do_QueryInterface(subject);
         if (uri && mConnMgr) {