Merge pull request #17 from Lekensteyn/fix-serviceworker-check

Fix fallback scripts when ServiceWorkers are unavailable

src/content/content.js

@@ -85,7 +85,7 @@ ns.on("capabilities", () => {
   
   if (!ns.canScript) {
 
-    if (!!navigator.serviceWorker.controller) {
+    if ("serviceWorker" in navigator && navigator.serviceWorker.controller) {
       addEventListener("beforescriptexecute", e => e.preventDefault());
       (async () => {
         for (let r of await navigator.serviceWorker.getRegistrations()) {