I am also getting the message Bad Request Your browser sent a request that this server could not understand. Size of a request header field exceeds server limit. This happens AFTER I log in to my account, when I try to look at my account balance or make a payment - or even when I try to log out. Interestingly it does not happen if I want to check something that requires a new tab to be opened. That works ok. All other sites are working correctly. My bank says it is most like an incompatibility with the latest version of Firefox - and can only offer the option to uninstall and reinstall Firefox or use another browser. (I have a back-up browser which does function properly.) I am running Firefox 75.0 on Windows 7 Professional - I have some work programs that don't work with more recent Windows versions. The last time I was able to use my internet banking through Firefox was 7th April.