The problem in firefox is from this bit of code:

    /*
        Darkmode
    */
    @media (prefers-color-scheme: dark) {
        html {
          background-color: white;
          filter: invert(100%);
        }

        input {
          filter: invert(20%);
        }
    }

It seems in firefox the invert doesn't apply to the background color of the html element so you end up with yellow on white.