You'll want to check if your browser is up-to-date, kastrup.

You can use the browser health checkup tool to see if your version of Mozilla Firefox is supported. QuickBooks supports the current and two previous versions of browsers. Old versions might cause errors and issues when using QuickBooks Online.

Check out this article for more information about supported browsers: System requirements for QBO.

Let me know if you have other questions, I'll be here to help.