Without seeing your CSS I can only assume you are using a webkit scrollbar (or some other sort of custom scrollbar) and Firefox doesn't support custom scrollbars to my knowledge.
Regarding scrollbars in IE, you can try to add this to your css:
html, body {
-ms-overflow-style: scrollbar;
}
The Bootstrap css that Mendix uses sometimes(?) causes IE10/11 to think it should use mobile scrollbar UI even on desktop. Here some more info on the topic. However I don't know why it's also happening to Firefox, and why the view is so different from Chrome there, haven't encountered that myself yet.