Assuming no special settings changes... Firefox keeps two lists of tabs: regular and private. If you close all the private tabs, Firefox should return to a regular tab (often the home screen). Tap the tabs button (icon with number on stack of squares) in the top bar to display the tabs list. If you were viewing a private tab, there will be a thick bar under the mask icon. To close all the private tabs, you can use the little "x" icons. Or to switch to the regular tabs list without closing the private tabs, you can tap the icon to the left of the mask, which looks like a little tab. Does it work normally so far?