Solved a bug where the options window was breaking the popup window. The issue was that some branches of the message handler in the background script weren't returning anything at all.

Shared (Extension)/Resources/manifest.json

@@ -12,8 +12,7 @@
         "512": "images/icon-512.png"
     },
     "background": {
-        "service_worker": "background.build.js",
-        "type": "module"
+        "page": "background.html"
     },
     "content_scripts": [
         {
@@ -48,7 +47,8 @@
                 "nostr.build.js",
                 "popup.build.js",
                 "options.build.js",
-                "options.build.css"
+                "options.build.css",
+                "options.html"
             ],
             "matches": [
                 "<all_urls>"