How can I prevent a user accessing the Library pop-up (Ctrl+Shift+o)

You can change or even clear it on about:keyboard.

Can I do this programmatically? Where do the settings get stored please?

Use this in your autoconfig (firefox.cfg): // Block Library page (Ctrl+Shift+O) Services.obs.addObserver((win) => {

 if (win.location.href.includes("places.xhtml")) win.close();

}, "domwindowopened", false); That’s the most reliable way on AppStream. If you want it even stronger, also hide the menu item with userChrome.css and globally block the hotkey at GNOME level. This should do it.

In the end I did this by:

• Added an event listener in an extension with the code:

// =========================================================================
 // 1. KEYBOARD LOCKDOWN
 // =========================================================================
 const ALLOWED_KEYS = [
   // New contexts
   { key: "f",   ctrl: true,                description: "Find" },
   { key: "r",   ctrl: true,                description: "Reload" }
 ];
 
 window.addEventListener("keydown", function (e) {
   for (const rule of ALLOWED_KEYS) {
     if (
       e.key        === rule.key       &&
       !!rule.ctrl  === e.ctrlKey      &&
       !!rule.shift === e.shiftKey     &&
       !!rule.alt   === e.altKey       &&
       !!rule.meta  === e.metaKey
     ) {
       return;
     }
   }
   
   if (e.ctrlKey || e.altKey) {
     e.preventDefault();
     e.stopImmediatePropagation();
     e.stopPropagation();
     return false;
   }

 }, true);

• Added to my userChrome.css:

/* Hide the Library Window Content (Bookmarks/History Manager) */ window#placesContext, window#places {

   display: none !important;
   visibility: hidden !important;

}

I'm investigating making some aspect of about:keyboard available to policy.

I'd love to talk more about what you're doing though.

Would you mind reaching out directly?

mkaply at mozilla.com