I add new elements to a list with form created with Infopath. Unfortunately, the Topnavigation bar is missing. Is there a way I could add it to my form page (newifs.aspx)?
It's the OOTB function to deploy the form like that, what you could do would be to create a blank page, edit the page and insert a InfoPath Form Web part and add your form there.
Then you can change the default list-form for the list to point to new page from the SharePoint Designer.