Cancel requests with the same requestId

Prevents potential redirects from opening two tabs
Closes #1114

src/js/background/assignManager.js

@@ -144,6 +144,21 @@ const assignManager = {
       return {};
     }
 
+    // we decided to cancel the request at this point, register it as canceled request as early as possible
+    if (!this.canceledRequests[options.requestId]) {
+      this.canceledRequests[options.requestId] = true;
+      // register a cleanup for handled requestIds
+      // all relevant requests that come in that timeframe with the same requestId will be canceled
+      setTimeout(() => {
+        delete this.canceledRequests[options.requestId];
+      }, 2000);
+    } else {
+      // if we see a request for the same requestId at this point then this is a redirect that we have to cancel to prevent opening two tabs
+      return {
+        cancel: true
+      };
+    }
+
     this.reloadPageInContainer(options.url, userContextId, siteSettings.userContextId, tab.index + 1, tab.active, siteSettings.neverAsk);
     this.calculateContextMenu(tab);
 
@@ -174,6 +189,7 @@ const assignManager = {
     });
 
     // Before a request is handled by the browser we decide if we should route through a different container
+    this.canceledRequests = {};
     browser.webRequest.onBeforeRequest.addListener((options) => {
       return this.onBeforeRequest(options);
     },{urls: ["<all_urls>"], types: ["main_frame"]}, ["blocking"]);