scrollbutton not hidden in multirow

[zolstarym]

Add all information required in 1-5 and delete this line and everything above it before submitting.

1. Describe the issue
   Scrollbuttons are not hidden when multirow is enabled:
   @import "./css/tabs/tabs_multiple_lines_fx71.css"; // /* Fx 71+ */
   see attached pic
   
   When the tabs reach the end of available space, the scrollbuttons appear above and below the tab bar.
   In tabs area on userchrome, @import "./css/tabs/tab_close_hidden.css"; // is also enabled
   and in general variables.css:
   /* for tabs_multiple_lines.css and tabs_multiple_lines_v2.css */
   --tab_min_width_mlt: 60px !important;
   --tab_max_width_mlt: 300px !important;

Using version 3.1.3

5. System information

• latest CustomCSSforFx files (yes / no [no support, if 'no']):
• OS & OS version:
  Linux mint 19.3
• OS theme (if not default):
• DPI / HiDPI resolution:
• Firefox version: 76
• Firefox theme / lw-theme:
• This projects 'settings' the issue occurs with:

[Aris-t2]

link[href$="arrowscrollbox.css"] ~ #scrollbutton-up,
link[href$="arrowscrollbox.css"] ~ #scrollbutton-down {
  display: none !important;
}

[zolstarym]

That fixes it. Thanks.