This is because kiwitrees uses the css “flex: box system to keep the footer always at the bottom of the screen, even when the page content is very short. Unfortunately old version of MS browsers either do not accept this style of do not treat it correctly. Thee are two solutions:
1 – the best solution in my opinion is not to use out-dated browsers. MS Edge is the only up-to-date MS browser (and the first EVER from them to get reasonably close to standard css acceptance) and should be used if you must use MS at all.
2 – If you or your users MUST use old browsers you can add one line to a mystyle.css file in your preferred theme. That line is:
body {display: block;}
It cancels the flex design code.