Maintenance for the week of August 31:
• NA megaservers for maintenance – August 31, 4:00AM EDT (8:00 UTC) - 12:00PM EDT (16:00 UTC)
• EU megaservers for maintenance – August 31, 8:00 UTC (4:00AM EDT) - 16:00 UTC (12:00PM EDT)
• ESO Store and Account System for maintenance – August 31, 4:00AM EDT (8:00 UTC) - 12:00PM EDT (16:00 UTC)
Check your settings in Firefox to see if one of them is causing an issue and if so, reset it to default. Also clear cache and cookies to see if that helps.