How can I fix my Windows 10 laptop's browser?

Firefox no longer works on Angela's machine and she has been forced to use Microsoft Edge. How can she fix it?

I cannot access various websites in Firefox. Some, like BBC News, will open but don't display correctly. More worryingly, I cannot sign in to my bank account or my credit card account on Firefox. I am forced to use Edge! I have run various scans with Kaspersky and Malwarebytes and don't know where to look next.

I have a Dell Inspiron 15 5000 laptop running Windows 10 Home, Firefox 61.0.2 and Kaspersky Internet Security. Angela

All software is corruptible and browsers, being complex, tend to suffer more than most applications. Problems may be due to corrupted user profiles, caches, or badly behaved extensions rather than the browser code, but for the user, the result is the same.