We typically see login issues related to blocked cookies in the browser extension.
In Firefox, this is usually the shield icon on the left side of the address bar (Enhanced Tracking Protection).
In Chrome, this is usually an eye icon in the address bar.
Turning these off should let the cookie save so you can log in. If that doesn't fix it, you can reset your password yourself (see How to reset or change your password) or let us know and we'll send you a reset email.