I could be mistaken but I believe currently the only CSS that mozilla supports for scrollbar styling is:
scrollbar-color: red green; (where red is the bar and green is thumb)
scrollbar-width: thin; (other option is thick)
There are some javascript scrollbar options that can be use to style Mozilla scrollers but I don't have much experience with them.
what you could do is something like:
@-moz-document url-prefix('') {
.ascenseur {
scrollbar-color: #7997cd green; (pick something not green)
scrollbar-width: thin;
}
This would apply the alternative style to mozilla (firefox) only and allow other browsers to use your original style.
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Scrollbars