Restrict cosmetic filter creation to the origin of the page it's on

components/brave_extension/extension/brave_extension/background/events/cosmeticFilterEvents.ts

@@ -63,8 +63,9 @@ chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
       break
     }
     case 'cosmeticFilterCreate': {
-      const { host, selector } = msg
-      applyCosmeticFilter(host, selector)
+      if (sender.origin) {
+        applyCosmeticFilter(new URL(sender.origin).host, msg.selector)
+      }
       break
     }
   }

components/brave_extension/extension/brave_extension/content_element_picker.ts

@@ -413,7 +413,6 @@ chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
       // Append the hostname and forward to the background script
       chrome.runtime.sendMessage({
         type: 'cosmeticFilterCreate',
-        host: window.location.host,
         selector: msg.selector
       })
       quitElementPicker()