Show Vertical Scrollbar in browser

in css file add:

html {
overflow-y: scroll;
}

for mozilla firefox, this:

html {
overflow: -moz-scrollbars-vertical;
}

always show vertical scrollbar!

For individual class , set overflow inside declaration:

.mayclass {
overflow-y: scroll;
}

Or you can rewrite default behavior elements , ex:

div { overflow-y: scroll; }