"page": "settings.html",
   "open_in_tab": true
 },"

   <script>
       function showPopup() {
           alert('Hello! This is a popup.');
       }
   </script>"

In about:config javascript.enabled = True I didn't change any settings there. If I place, for example, '' " "options_ui": { "page": "settings.html", "open_in_tab": true },"'' in the manifest.json of the extension, it does open the settings.html page as intended. Problem is that no JS script on settings.html works, be it if it's inline HTML or as a separate file (I tried separate file, as I thought it might be a security thing). I mean even simple JS such as console.log or '' "<button onclick="showPopup()">Show Popup</button> <script> function showPopup() { alert('Hello! This is a popup.'); } </script>"'' Other actually installed extensions - their JS on settings pages runs. I also tried running settings.html as a popup, and I succesfully done so, it's just that once again JS didn't work... I'm at my wits end, I have googled, I have chatted with the ChatGPT, took me hours thinking it was something wrong with my code... I'm actually making something useful, never done before (it reads out youtube subtitles via TTS, providing ability to still hear original sound, its emotions, no need to look at the screen and it's also a passive language learning type of thing), and it works, it's just that setting page's JS, which I think I need to allow users change speed of TTS and volume of the TTS