This is an online app intended to be working within your browser. Hence it requires a browser like Chrome or Internet browser to make changes.
However to view the map outside a browser, there are a couple of choices.
i. To export the map as a picture. Use 'Document'->'Export as a Image' to save it as an image file.
ii. Export it as a Adobe PDF file. See this article for more detail, http://mindmapmaker.org/export-mindmap-as-pdf-using-chrome.html