I have had to go to Microsoft Edge as that allows me to log in as usual

I have been using Firefox to login to sites for years with no problems. Within about the last 7 days I have been unable to use Firefox for some of these sites. I input the sign ins and password and the details vanish and the page reverts to asking for log in details. Normally the sites would request a 'phone call after 3 false attempts, but this is not happening. I have had to go to Microsoft Edge as that allows me to log in as usual Please can you help?