feat: add UI toast notification for missing Firefox browser

app/toastNotifier.js

@@ -0,0 +1,22 @@
+const {getMainWindow} = require("./windowManager");
+
+/**
+ * Sends a toast notification to the renderer UI when the main window is ready.
+ *
+ * @param {string} message
+ * @param {"success"|"error"|"warning"|"info"} [type="info"]
+ * @param {number} [duration=4000]
+ * @returns {boolean} Whether the toast was sent.
+ */
+function sendToast(message, type = "info", duration = 4000) {
+    const mainWindow = getMainWindow();
+
+    if (!mainWindow || mainWindow.isDestroyed() || mainWindow.webContents.isDestroyed()) {
+        return false;
+    }
+
+    mainWindow.webContents.send("show-toast", {message, type, duration});
+    return true;
+}
+
+module.exports = {sendToast};