You may run into trouble if you keep more than one copy of Fargo open at a time on the same computer. You should get error dialogs warning you before you overwrite an existing file with an older version. But the best way to operate is to keep at most one tab with Fargo open at any time.
If you open Fargo and find there are no tabs visible, try this. Go to the Fargo folder. Open the #prefs folder. Delete tabs.json. Back in the browser, reload the Fargo page.
Reload often. It's the cure for a lot of problems. It also helps make sure you're running the latest version.
Try signing out. The command is in the System menu (the rightmost one, labeled with your Dropbox username). When you choose the command you'll get a dialog directing you to give permission in Dropbox.
When you choose the View in Reader command in Fargo, your browser may prevent it from opening, thinking we're opening a popup window (because that's what it may look like to the browser). Usually the browser offers you the option to open the window anyway, but you may have to look for the option (in Chrome for example, it's in the right edge of the address area at the top of the browser window).