Can't login using Firefox

Question

I can't log in on any of ETC pages (forum, learning, etc) since some days ago using firefox browser (version 91.0.2).
I am using Safari andit works fine.
Any idea why this is happening?
MacBook Pro 2,5 GHz Quad-Core Intel Core i7

Drew Fabian · Answer

Just leaving a brief update here for anyone else watching this thread, as the issue seems to have been resolved after a few more emails between Tom and I. 
 The root cause ended up being a subtle difference in how FireFox and Safari send HTTP headers with requests. A firewall rule was being triggered which was flagging the login attempts as malicious activity. 
 The firewall rule itself was not applicable to our setup, and so we disabled the rule and the sign ins started working again. 
 Warm Regards, 
 Drew