Those layout.css prefs are about enabling some CSS feature, in this case vertical writing, so have n

Those layout.css prefs are about enabling some CSS feature, in this case vertical writing, so have nothing to do with scroll bars.

Bug 772321 - implement CSS parsing of writing-mode property

resource://gre/greprefs.js

// Is support for CSS vertical text enabled? pref("layout.css.vertical-text.enabled", false);

Can you attach a screenshot?

http://en.wikipedia.org/wiki/Screenshot

https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Use a compressed image type like PNG or JPG to save the screenshot.