Since yesterday, I have been unable to use Firefox to sign into my online banking and keep getting a sign in error message

I have been using Mozilla Firefox and Thunderbird for several years without any problems. Since yesterday, on trying to log into my online banking accounts, I keep getting a sign in error message. I have checked with my bank and the error does not lie with their website or my user name and password. I am able sign in successfully using Internet Explorer. I have tried uninstalling Firefox and then downloading the latest version from your website but this has made no difference