Document editor: creating new documents results in blank page

When creating a new Onlyoffice document a new browser tab opens. The first time it remains blank and the dialog in the original tab remains open. After a while Firefox in my case, asks me to allow opening new windows. If I allow that everything works but two new tabs are opened. A blank one and one with the editor opening inside. This might be okay but the very first opening of a document is confusing.

(even Sabine was confused )