I just had the same problem with IE, menus disappeared, traffic graphs stopped working, dashboard -> system info -> version was stuck on 'Obtaining update status …' and cpu usage was stuck on '(Updating in 10 seconds)'. In the meantime everything was working fine in Chrome. It turns out I had accidentally toggled compatibility view in IE, toggled it back and everything started working again. Not sure how well known this is, I'm fairly new to pfsense.