fix(firefox): inject script into page context to avoid DeadObject issue

Recent Firefox update caused cross-window access issues.
Injecting the script into the page context resolves this.

extension/load.js

@@ -0,0 +1,8 @@
+function loadScript(url) {
+    let script = document.createElement("script");
+    script.src = browser.runtime.getURL(url);
+    document.documentElement.appendChild(script);
+}
+
+loadScript("lib/jquery-3.7.1.min.js");
+loadScript("carbon-for-f1tv.user.js");

extension/manifest_firefox.json

@@ -17,7 +17,7 @@
           "matches":[
             "https://f1tv.formula1.com/*"
           ],
-          "js": ["lib/jquery-3.7.1.min.js", "carbon-for-f1tv.user.js"]
+          "js": ["load.js"]
         }
       ],
       "browser_action": {