Sometimes Firefox can prevent users from signing in to StudioBinder. This can easily be solved by clearing old site data that's stored in the browser.
Remove Cookies from Firefox
In Firefox's menu bar, click on Firefox > Preferences
From the sidebar, select Privacy
In the History section, click the drop down next to Firefox will:
In the dropdown, select "Use Custom Settings for History"
Click the Show Cookies... button
In the pop-up, search for StudioBinder
Select StudioBinder from the list, and click Remove Selected
After that, refresh StudioBinder, and try signing in again.
Note: Here is an article that can help if you are having issues printing with Firefox.